Mountain, Alaskan, and Hawaiian zones are either on their own to delay broadcast by an hour or two, or collectively form a small, regional network feed with others in the same time zone. Prime time is commonly defined as 8:00–11:00 p.m. Eastern/Pacific and 7:00–10:00 p.m. Central/Mountain. On Sundays, the major broadcast television networks traditionally begin their primetime programming at 7:00 p.m. (Eastern/Pacific, 6:00 p.m. Central/Mountain). Some networks such as Fox, The CW, and MyNetworkTV broadcast only from 8:00–10:00 p.m., a time period known as "common prime". Most networks air primetime programming nightly, but the smaller MyNetworkTV has programmed only on weekday evenings since its 2009 retreat towards a programing service. The CW returned to Sunday broadcasting in 2019, then added Saturday for the first time in 2021. In Canada, CTV and Global both follow the same model as the larger U.S. networks (although both may occasionally air programming in the 7:00 p.m. hour in the event of scheduling conflicts with other U.S. imports), while CBC Television, Citytv and CTV 2 schedule prime-time programs only within the common prime period (with the 10:00p.m. hour dedicated to syndicated programming on Citytv and CTV 2, and CBC airing its news program The National). The Canadian Radio-television and Telecommunications Commission (CRTC) has alternatively defined prime time as ranging from 6 pm to 11 pm to 7 pm to 11 pm. Since the early 2000s, the major networks have come to consider Saturday prime time as a graveyard slot, and have largely abandoned scheduling of new scripted programming on that night. The major networks still maintain a prime-time programming schedule on Saturdays, with a mix of live sporting events (most commonly college football in the United States and ice hockey in Canada), encores of programs aired earlier in the week, films, non-scripted reality programs, true crime programs produced by their news divisions and, occasionally, burning off episodes of low-rated or cancelled series. Prime time can be extended or truncated if coverage of sporting events run past their allotted end time. Since the "Heidi Game" incident in 1968, in which NBC cut away from coverage of a New York Jets/Oakland Raiders football game on the east coast in order to show a movie (and, in the process, causing viewers to miss an unexpected comeback by the Raiders to win the game), the present-day National Football League mandated that all games be broadcast in their entirety in