Effects of time zones on North American broadcasting
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The scheduling of television programming in North America must cope with ten time zones: the United States (excluding territories) has six time zones (Hawaii-Aleutian, Alaska, Pacific, Mountain, Central and Eastern), with further variation in the observance of daylight saving time; Canada also has six (Pacific, Mountain, Central, Eastern, Atlantic and Newfoundland); Mexico has three (Pacific, Mountain and Central); Greenland also has three (Atlantic, UTC−03 and UTC−01; UTC−02 is not used). This requires broadcast and cable television networks in each country to time-shift programs shown in different regions.
Canadian broadcasting networks, with six time zones and a much larger percentage of its audience residing in the Mountain Time Zone than in the Central Time Zone, are sometimes able to avoid the issues that affect U.S. programming by airing prerecorded programs on local time. CBC Television and CTV created delay centres in Calgary, Alberta in the early 1960s in order to allow programming to air in each time zone based on the region. The sole exception is in Newfoundland and Labrador, which has a time zone oddity of running a half-hour later than the nearby Maritimes region. This is particularly a problem in Saskatchewan as most of the province does not observe daylight saving time and remains on Central Standard Time year-round. While Saskatchewan, Manitoba and parts of northwestern Ontario share the same clock setting during the winter season, Saskatchewan and Alberta share the same clock setting during the summer season, despite the fact that Alberta is in the Mountain Time Zone. Schedules must therefore be adjusted for the summer season in some areas.
In the vast majority of cases, local time schedules on CBC Television stations (and, for that matter, the CBC's radio networks) are identical in all markets, except for certain types of live programming and the aforementioned oddity of the Newfoundland Time Zone; CBC stations in Newfoundland use the same network feeds as the Maritimes so programs are scheduled for 30 minutes "later" than other parts of the country.
However, particularly among private broadcasters, there are often significant variances in local schedules from one time zone to the next due to the preference for showing U.S. programs at the same time as the U.S. network affiliates available through local cable and satellite providers, which maintains a Canadian broadcaster's right to simultaneous substitution. This is further complicated by the fact that the affiliates available are not necessarily from the same time zone: the easternmost time zone in the U.S. is the Eastern Time Zone, so viewers in Atlantic Canada always receive American network affiliates from that time zone. Meanwhile, even though there are U.S. network stations in the Mountain Time Zone (which normally air network programs from 7 to 10 p.m. local time), for reasons unknown the American stations available in Alberta have always come from the Pacific Time Zone. Hence in both the Atlantic and Mountain time zones, U.S. "prime time" actually runs from 9 p.m. to midnight.
Accordingly, while private Canadian networks have generally adopted the U.S. practice of broadcasting simultaneously to the Eastern and Central time zones ("8, 7 Central"), in recent years they have standardized on a different approach for stations in the Atlantic and Mountain time zones. In these markets, U.S. programming will run in simulcast between 9 and 11 p.m. local (8 to 10 on the U.S. stations being simsubbed), while the U.S. "10 p.m." program, despite often being dramatically darker or more adult in tone, will usually air earlier in the evening at 8 p.m. local time. In the case of lengthy events such as movies or awards shows which extend into the 10:00 p.m. ET/PT hour, the program will usually be scheduled to air within the local primetime block if possible (although surrendering any local simsub privileges for that program in the process) or simply aired to its conclusion in the case of live events (particularly in the Atlantic time zone). In Newfoundland, the lone local private station CJON-DT currently follows the lead of its Maritime counterparts in most cases, but again with a further 30-minute "delay" for Newfoundland Time.
A small number of Canadian television networks are not broadcast to a national audience such as over-the-air networks CTV Two and City – which air only in certain markets and do not have stations in the Yukon, Nunavut and Northwest Territories – and premium cable channels Movie Central and The Movie Network – which air in separate areas of Canada (Movie Central in the Territories and Western Canada and The Movie Network in Ontario, Quebec and Atlantic Canada). Such channels may not require significant timeshifting, as they only cover a few time zones instead of serving all six time zones that serve the country. Télévision de Radio-Canada, the French counterpart of CBC Television, has four feeds to allow programs to air at the same time in each zone's local time, except for the Atlantic and Newfoundland time zones, which air programs at the same time as in the Eastern Time zone, but 60 and 90 minutes later respectively on their clocks (e.g. 20h00 HE/21h00 HA/21h30 HT).
Some specialty cable and satellite television channels in Canada have two broadcast feeds for Eastern and Western Canada (such as YTV, Teletoon and The Comedy Network). The Eastern feed airs programs on an Eastern Time schedule, while the Western feed airs the same programming three hours later on Pacific Time. The separation between feeds is typically implemented at the border between Manitoba and Ontario, however one channel, the Aboriginal Peoples Television Network, implements the separation at the border between Manitoba and Saskatchewan. All other specialty cable channels have one feed for all time zones, including French language channels that predominantly serve Francophone areas of the country, mostly in Quebec.
The UTC−03:00 Standard Time Zone is commonly used as a de facto official time by the Greenlander main broadcasting station Kalaallit Nunaata Radioa; there are three time zones but most of the island's population resides in the UTC−03:00 zone, which covers the central one-third of Greenland. Thus broadcasters sometimes avoid timeshifting issues by airing programs on UTC-03:00 time. This is a problem in the eastern town of Ittoqqortoormiit as the settlement and its surrounding area uses UTC−01:00 Standard Time Zone. Both time zones observe daylight saving time with European Union DST rules.
The UTC−04:00 Standard Time Zone is used in northwestern Greenland, and the area around Thule Air Base observes North American DST rules, known in Canada as the Atlantic Time Zone and in the Caribbean as the "Eastern Caribbean Time Zone". The UTC−02:00 Standard Time Zone is not used.
The Central Time Zone is commonly used as a sort of de facto official time for the Mexican broadcasting networks, with three time zones to span. Since a much larger percentage of its audience resides in the Central Time Zone than in the Mountain Time Zone, broadcasters often air their programs on Central time. This is particularly a problem in Sonora as the whole state does not use daylight saving time and remains on Mountain Standard Time year-round (this matches the practice of Arizona, with which it shares an expansive border). The thinly-populated Revillagigedo Islands do not use daylight saving time and remain on Mountain Standard Time year-round, with the minor exception of Clarion Island which remains in the Pacific Standard Time year-round.
When the U.S. extended its daylight time period in 2007, Mexico did not change its effective dates. This means that in most of the country, daylight saving time starts three or four weeks later and ends one week earlier than in the U.S. and Canada. However, the northern border cities in four of the six states that border on the U.S. (Chihuahua, Coahuila, Nuevo León and Tamaulipas), plus the entire state of Baja California, activate daylight saving time on the same dates as the U.S. and Canada. During the period when the U.S. and Canada are on daylight saving time and most of Mexico is not:
- Baja California is one hour behind Mexico City;
- The northern border cities of Chihuahua have the same time as Mexico City;
- Northern border cities in Coahuila, Nuevo León and Tamaulipas are one hour ahead of Mexico City.
United States 
Time zone feeds 
With four time zones in the contiguous United States, U.S. national networks and cable channels generally air at least two separate feeds to their stations and affiliates: the "east feed" that is aired simultaneously in the Eastern and Central Time Zones, and the "west feed" that is tape-delayed three hours for those in the Pacific Time Zone. This ensures that a program, for example, that airs at 8 p.m. on the east coast is also shown locally at 8 p.m. in the Pacific states. Networks may also air a third feed specifically for the Mountain Time Zone, which usually airs on a one-hour delay from the east feed; otherwise those in the Mountain Time Zone get the west feed.
The Eastern Time Zone is commonly used as a de facto official time for the United States – since it includes the nation's capital Washington, D.C., the country's largest city, New York and nearly half of the country's population. Because of this, television schedules are almost always posted in Eastern Time. Broadcast networks and cable channels also advertise airtimes in Eastern time, sometimes also including either Central or Pacific time and until the 1980s, Mountain time, depending on whether there is a separate feed for that time zone. This has led to conventions like "tonight at 9/8 Central" (referring to the east feed), "tonight at 9 p.m. Eastern and Pacific" (referring to both the east feed and the three-hour delayed west feed), and "tonight at 9/8 Central and Mountain" (also including the Mountain feed).
A few cable channels may not audibly refer to the Central time airtime of a program, though their promos may also visually include references to its broadcast in both the Eastern and Central time zones. So when a viewer only hears "tonight at 8," regardless of whether the promo visually includes it or not, chances are that the show they are referring to is scheduled to air at 7 p.m. in the Central time zone.
Broadcast television 
Effectively, the East, Mountain and West feeds allow primetime on the over-the-air broadcast television networks to end at 10 p.m. Central and Mountain and 11 p.m. Eastern and Pacific – though Fox, The CW and the MyNetworkTV program service subtract an hour for their primetime schedules as they end their evening network programming lineup earlier than NBC, CBS and ABC.
For some shows, the networks must utilize a fourth feed for the Central Time Zone. Morning shows like Good Morning America, Today and CBS This Morning may start too early for viewers in the Midwest and the central South; hence, they are tape-delayed to air at 7 a.m. Central Time. In another example, Dick Clark's New Year's Rockin' Eve with Ryan Seacrest, which airs every New Year's Eve, must be broadcast so that the show is correlated to when midnight strikes in every time zone.
In 2009, PBS began using servers instead of separate feeds for time delaying of its programming to the network's member stations, the servers imitate a delayed program feed, broadcasting the program at the correct airtime as if it were being broadcast via satellite. This was done as PBS had upgraded its main program feed to high-definition (or to widescreen digital at the very least) in December 2008, but satellite capacity allowed for only Eastern and Pacific time zone feeds, prompting the removal of the feeds for the Central and Mountain time zones and a shared feed for Alaska and Pacific time zones in February 2009, which created complaints from PBS stations.
Network programming in Alaska generally follows a schedule similar to that of Central Time Zone, with stations in Anchorage broadcasting directly from the Pacific time zone feed without tape delay. Programs that air at 8 p.m. Pacific will air at 7 p.m. in Anchorage and Juneau. With the exception of ABC affiliate KATN, network programming in Fairbanks is tape-delayed by one hour. Hawaii also follows a schedule similar to the Central Time Zone (though Fox affiliate KHON-TV and its satellites air the network's Sunday programming on a one-hour tape delay, airing from 7-10 p.m. instead of 6-9 p.m.).
The territory of Guam, which is on the other side of the International Date Line from the rest of the United States, airs primetime shows, network newscasts and morning shows the day after they air in the U.S. off a satellite feed. However, sports events air live; those that air in the daytime in the U.S. show overnight in Guam, while NBC Sunday Night Football, the World Series and other primetime telecasts air the next morning, typically at 9 or 10 a.m. The only network affiliate in American Samoa, KKHJ-LP, airs the Pacific time zone feed on a three-hour delay (details for Puerto Rico and the Virgin Islands are in the next section below).
Not all network programming is strictly scheduled, however. Network soap operas, game shows and national news programs have recommended times to air, but the final scheduling for those shows is most often at the discretion of the local stations.
Cable and satellite television 
Subscribers of cable or satellite television services may still only receive the East Coast Feed for certain channels even if they reside on the West Coast. Some cable channels may in fact only offer one feed to begin with, meaning viewers see the same program in all time zones (for example, when WGN America airs the 9 p.m. CT newscast from WGN-TV in Chicago, the program also airs at 10 p.m. ET in Washington, D.C. and 7 p.m. PT in San Francisco).
On the other hand, some providers may offer both the East and West coast feeds of some basic cable channels for viewing in all time zones, allowing viewers who missed a particular program to watch it three hours earlier or later depending on the time zone they live in. Nickelodeon is the only U.S. basic cable channel that airs dual broadcast feeds to viewers who do not subscribe to satellite television, as that channel offers an alternate feed known as Nick 2, which is essentially the opposite coast's feed of Nickelodeon (the Pacific time zone feed for East Coast viewers, and vice versa) to digital cable subscribers – while the channel's main feed for the respective time zone is carried on the local cable provider's basic package.
The usage of dual feeds of the same channel is a commonplace method for premium channels such as HBO, Showtime and Starz, in which the Pacific time zone feed of (usually only) the primary channel is packaged with the East Coast feed of the main channel and the pay service's multiplex channels (if the premium channel has any). In some cases, cable networks (such as cable news and sports channels) "fake" the dual feed approach by recycling their same-day prime time programming during the overnight hours on a three (or four) hour cycle; in this case, the programs are automatically rebroadcast at the advertised time (or one hour later) in the Pacific time zone.
Live events 
Many national live events though are broadcast simultaneously nationwide – including most sporting events, national breaking news stories, the State of the Union address, presidential and Congressional election coverage and certain award shows (such as the Academy Awards). Live events that are simulcast across the country also present special problems for local stations; for such events the networks may either advertise Eastern time only, or list the times in both Eastern and Pacific (e.g. "8 p.m. Eastern/5 p.m. Pacific"). As such, a live Sunday sporting event that is played from 4 to 7 p.m. Eastern Time preempts local 6 p.m. newscasts on the East Coast. Likewise, a State of the Union address that is televised at 9 p.m. Eastern Time preempts local 6 p.m. newscasts on the West Coast.
However, many award shows, most Olympic competitions and other similar events that are broadcast live in the Eastern and Central time zones, including some that originate from Los Angeles (such as the Grammy Awards and certain reality competition shows such as Dancing with the Stars and the final rounds of American Idol), may be tape-delayed in the Mountain and Pacific time zones, thus making it impossible for viewers in those time zones to vote after performance episodes of live reality competition shows finish airing on the East Coast. The practice of tape delay is due to the potentially higher West Coast viewership during primetime hours, and also allows potentially objectionable content occurring without warning that is not allowed on broadcast television per FCC regulations (such as fleeting profanities or wardrobe malfunctions) to be edited out for broadcast in the Mountain and Pacific time zones, if they are shown live on the East Coast feed. When programs such as these air on tape-delay to other time zones, it is not uncommon for networks to display a graphic at the beginning of the broadcast stating that the program being shown is "recorded from an earlier live broadcast" or simply "recorded earlier". As well, when one of these program's graphics may include the display of the word "live" on screen, networks may add the letters "EST" or "EDT" (depending on whether or not the country is on Standard or Daylight Saving Time at the time of the broadcast) as a way of advising viewers in other time zones that the "live" broadcast they are watching is actually pre-recorded, and only aired live in the Eastern time zone (this is a common practice with tape-delayed broadcasts of American networks' morning programs).
Similarly, media coverage of New Year's Eve celebrations in New York City often leave the Central Time Zone out. Late Night with Conan O'Brien, though produced in New York, when broadcast on New Year's Eve took advantage of its later time slot (11:37 p.m. Central time) to lampoon this inconsistency and produced its own New Year's countdown for television viewers in the Central Time Zone, although most Central Time local network affiliates usually broadcast Conan after covering their own regional New Year's Eve celebrations. In some locations, New Year's Eve celebrations held in New York might be repeated or delayed one hour to correspond to the Central Time zone. News channels such as CNN and sports channels such as ESPN that frequently broadcast live events offer a single feed that airs in all time zones. About 80 percent of American television viewers reside in the Central and Eastern time zones.
Effects on local programming 
Local stations and affiliates must schedule their local and syndicated programming around their respective network's feed. Because primetime programs on the East Coast Feed is simulcast in two time zones, it affects stations in the Central Time Zone differently than those in the Eastern Time Zone. An hour of syndicated programming time (between 7 and 8 p.m. in the Eastern and Pacific time zones) is lost in the Central and Mountain time zones since network primetime in those areas starts at 7 p.m., forcing stations in Mountain or Central time (or in parts of both zones) to choose between airing their 6 p.m. newscast and another syndicated or locally-produced program, or airing shows in 'blocks' preferred by syndicators (for example, Wheel of Fortune and Jeopardy! together, or Entertainment Tonight and omg! Insider).
The most common set of programming chosen by stations aligned with the Big Three television networks (ABC, CBS, and NBC) is to air a newscast at 5 p.m., national news at 5:30 p.m., local news at 6 p.m. and syndicated programming at 6:30 p.m., though some Fox stations that carry a newscast schedule comparable to stations tied to the Big Three (commonly stations that were former ABC, NBC and CBS affiliates themselves) carry a 60- or 90-minute block of news from 5-6 (or 6:30) p.m. with an additional half-hour of local news in the 5:30 p.m. timeslot since Fox does not air a national evening newscast. Most Big Three affiliates in the Eastern and Pacific time zones follow this early evening newscast model as well, running a 90-minute block of news from 5-6:30 p.m., particularly if they run a network's national evening newscast at 6:30 p.m. ET/PT. Some stations, regardless of time zone, even show a newscast from 6-7 p.m., which if run on a network station in the Central or Mountain time zones would lead into primetime network programming. Some television stations (such as WKYC and WJW-TV in Cleveland or WJAR in Providence, Rhode Island) have recently begun using the fact that primetime in the Eastern time zone begins at 8 p.m. to their advantage by carrying a newscast during the 7 p.m. hour, generally in order to attract viewers who work longer days and cannot return home to watch a 5 or 6 p.m. newscast.
Many stations that do not carry a newscast in the 6 p.m. time slot in the Central time zone (commonly affiliates of non-historical networks like Fox –though some Fox stations air a 6 p.m. newscast, though this is not entirely commonplace – The CW and MyNetworkTV) air situation comedies or other types of syndicated programming such as reality series during that hour. Many stations in the Central Time Zone tend to air one or both parts of the syndicated block at 5 p.m. or even earlier. Another more recent dilemma of the 7 p.m. primetime start is that a combination of longer commutes and work hours than in the past have caused many people to not come home from work until after 7 p.m., cutting into the potential ratings of shows that start at this time. Of course, the reverse is also true, as simultaneous broadcasts offer viewers the chance to watch "prime time television" without having to stay awake until 11 p.m.
Local programming and television news are not typically affected as many stations air their morning newscast at 4:30, 5 or 5:30 a.m., and their early evening newscasts at 5 and/or 6 p.m.; the late evening newscast is affected due to the differences in time between time zones, meaning that if the late local news starts at 10 p.m. Central time on one network station, an affiliate of the same network in the Eastern Time Zone airs its newscast at 11 p.m.; the late night program lineups on NBC, ABC and CBS are also similarly timeshifted airing a half-hour later. Many Fox, CW and MyNetworkTV affiliates and some independent stations carry a prime time newscast that is similarly affected by the timeshifting of the primetime schdule, meaning that if the primetime local news starts at 9 p.m. Mountain time on one network station, an affiliate of the same network in the Pacific time zone would air its news at 10 p.m.
Changes for Daylight Saving Time 
Time changes for daylight saving time may result in broadcast television stations and cable channels accommodating the time changes by altering their schedules to allow programs to continue to air at the same time year-round. Since 2007, daylight saving time begins on the second Sunday in March and concludes on the first Sunday in November; due to the structure of daylight saving time (which begins and ends at 2 a.m. in each time zone on the respective dates), the switch from standard time requires clocks to be advanced by one hour to 3 a.m., and the reversion to standard time requires clocks to be moved back by one hour to 1 a.m.
During the switch from standard time to DST, television stations and cable networks will usually offset the loss of one hour by eliminating programming otherwise scheduled during the 2 a.m. hour for that week. Conversely, as one hour is gained when reverting to standard time, networks may offset the time change by adding an hour of additional entertainment programming not normally scheduled on Saturday nights/early Sunday mornings the rest of the year to allow certain programs to air at their regularly scheduled airtime (e.g., Disney Channel will add an hour of its original series at 1 a.m. EDT in order to allow its Saturday late night film block to air its regular 2:30 a.m. slot, after the reversion to standard time). Cable channels airing paid programming during the late night period may choose not to add entertainment shows and instead add an additional hour of infomercials (e.g., Discovery Channel usually extends its infomercial block, which normally begins at 3 a.m. ET, by one hour; similarly, E! adds one hour of infomercials in the 2 a.m. EDT slot, normally ceded to general entertainment programming, followed by one hour of entertainment programs, then a block of infomercials starting in their normal 4 a.m. EST slot).
Some areas of the U.S. do not observe daylight saving time, leading to the following changes; though in all cases, sports and other event telecasts that are broadcast live always begin an hour earlier, depending on time zone:
- Stations in Arizona (only the Navajo Nation observes DST) change from the live Mountain Time feed to a delay from the Eastern/Central feed when DST begins, to preserve a 7 p.m. start time. This is also the case for live syndicated radio programs such as The Rush Limbaugh Show, which air live during the winter and are delayed one hour during DST;
- Shows airing on stations in Puerto Rico and the United States Virgin Islands during DST start at the same time as Eastern and Central Time. Otherwise, primetime is on a one hour delay. This is because affiliates there receive their programs from the ET/CT master control (a similar arrangement occurs in Bermuda, which is a British territory but is the home of two affiliates of U.S. networks);
- In Alaska, Hawaii, Guam and American Samoa, primetime shows are delayed by an additional hour.
Scheduling variations for areas located between two time zones 
A handful of U.S. media markets lie on bordering time zones (Pacific/Mountain, Mountain/Central or Central/Eastern). While stations will carry a program in all counties part of the Designated Market Area, counties on either side of the market will air network programming simultaneously one hour earlier or later, depending on location:
- A number of media markets based in Eastern Time Zone cities have outlying areas in the Central Time Zone, including Atlanta and Columbus, Georgia, Louisville, Kentucky, Knoxville, Tennessee and Terre Haute, Indiana. However, since the usual primetime lineup is fed to them at the normal times for their zones, the effects are minimal in contrast to the following examples.
- Fox affiliate KECY-TV (and its ABC-affiliated subchannel), which are licensed to El Centro, California, start primetime programming at either 6 or 7 p.m. local time, depending on Daylight Saving Time status, because Yuma County in Arizona shares a media market with El Centro. All other stations in California start primetime network shows at 8 p.m.
- Satellite stations in western North Dakota, within the Mountain time zone, have 6 p.m. starts to primetime rather than the usual 7 p.m. because the primary stations are in either Bismarck or Minot in the Central time zone. These stations also serve areas in eastern Montana, which also observes the Mountain time zone.
- The four counties in western Kansas which observe Mountain Time receive prime-time programming from 6 to 9 p.m. since they are part of the Wichita DMA and the stations are satellites of the main feed in Wichita.
- Viewers in Lincoln County, Montana receive primetime shows from the Spokane, Washington DMA two hours later than locations elsewhere in the Mountain Time Zone – from either 9 p.m. to 11 p.m. (or midnight) MT Monday through Saturday and 8 p.m. to 11 (or midnight) on Sunday, depending on the network.
See also 
- "Half an hour later in Newfoundland....?" Yes, but why?"
- Based on the 2011 population estimate, 46% of the nation's population (in the contiguous states) live in the Eastern time zone, 30% in the Central zone; 7% in the Mountain zone, and 17% in the Pacific zone.
- "New servers, not separate feeds, will handle PBS time-zone delays (Idaho Public Television in the News)". Idahoptv.org. Retrieved 2012-10-25.
- "SouthCoastToday.com — News Archive — Your link to SouthCoast Massachusetts and beyond". Archive.southcoasttoday.com. 2012-10-15. Retrieved 2012-10-25.
- Lynette Rice (February 22, 2012). "Oscars exec producer: 'We need to go for comedy'". EW.com (CNN). Retrieved 2012-02-22.