Mountain Time Zone is generically called Mountain Time (MT). Specifically, it is Mountain Standard Time (MST) when observing standard time, and Mountain Daylight Time (MDT) when observing daylight saving time. The term refers to how the Rocky Mountains, which range from northwestern Canada to the US state of New Mexico, are located almost entirely in the time zone. In Mexico, this time zone is known as the Zona Pacífico (Pacific Zone). In the US and Canada, the Mountain Time Zone is to the east of the Pacific Time Zone and to the west of the Central Time Zone. In some areas, starting in
Prime Time Access Rule hour of prime time (7:00–8:00 p.m. Eastern Time and Pacific Time, 6:00–7:00 p.m. Central, Mountain, Alaska and Hawaii–Aleutian Time) as the "prime access hour". By the early 1980s, the PTAR had introduced a policy amendment prohibiting stations in the 50 television markets with the highest prime time viewership from broadcasting more than three hours of network programming during the four-hour "prime time" block. Stations had to find original programming to fill during the "prime time" fraction. However, the rule exempted certain types of programming, such as overruns of live sports events, special news, documentary and children's programming, and certain sports