From Wikipedia:
Today (also referred to as The Today Show) is an American morning news and talk show airing every morning on NBC. Debuting on January 14, 1952, it was the first of its genre, spawning similar morning news and entertainment television programs across the United States and around the world. The show is also the third-longest running American television series. Originally a two-hour program on weekdays, it expanded to Sundays (currently one hour) in 1987 and Saturdays (two hours) in 1992. The weekday broadcast expanded to three hours in 2000, and a fourth hour launched in 2007.
The show's first broadcast aired on January 14, 1952. It was the brainchild of Sylvester L. Weaver, Jr., who was then vice-president of NBC. Weaver was president of the company from 1953 to 1955, during which time Today's late-night companion The Tonight Show premiered. In pre-production, the show's proposed title was The Rise and Shine Revue.
Today was the first show of its genre when it signed on with original host Dave Garroway. The show blended national news headlines, in-depth interviews with newsmakers, lifestyle features, other light news and gimmicks (including the presence of the chimpanzee J. Fred Muggs as the show's mascot during the early years), and local station news updates. It has spawned several other shows of a similar type, including ABC's Good Morning America, and CBS' The Early Show. In other countries the format was copied – most notably in the United Kingdom with the BBC's Breakfast and ITV's Good Morning Britain and in Canada with Canada AM on CTV.
When Today started, it was seen live only in the Eastern and Central time zones, broadcasting three hours per morning but seen for only two hours in each time zone. Later, Today aired live for five hours a morning on Monday morning, but it was seen for only two consecutive hours in each of the four U.S. continental time zones. Since 1958, Today is tape-delayed for the different time zones. For many years it was a two-hour program from 7:00 a.m. to 9:00 a.m. in all time zones except for Alaska, Hawaii and U.S. Virgin Islands, until NBC expanded it to three hours on October 2, 2000. A fourth hour was added on September 10, 2007. In some markets (such as Boston, Massachusetts, on WHDH-TV), the third and fourth hours of Today are aired on further tape delay.
During the first three hours, local affiliates are offered a five-minute window at :25 and :55 to insert a local newsbreak, although the show provides additional segments for those affiliates who do not do so.
When breaking news stories warrant, Today will broadcast a live West Coast edition. The live updates typically do not last longer than the 7:00 a.m. (PT) hour and once completed, will return to the taped East Coast feed. When the anchors welcome the viewers to the show, they will note the current time as being "Pacific Time" and continue to note it as such until the tape delay is started. In some instances, when NBC Special Reports occur during the Today timeslot, the show's anchors will assume hosting responsibilities.