A bit of trivia: when the two coasts were joined on September 4, 1951, there were 107 stations on the air (the last pre-freeze licensee, Atlanta's Ch. 11, then WLTV Ch. 8, would sign on Sept. 30). One station, however, was not linked into the system: KOB Albuquerque, and I don't know when it was. To mark the occasion, President Harry S Truman addressed the UN, then still headquartered in San Francisco, and Douglas Edwards began using his longtime opening, "Good evening everyone, from coast to coast." Still, there was some crazy scheduling in those early days; I once posted a retro for San Francisco for a Monday in 1951; KPIX carried the live feed of "Arthur Godfrey's Talent Scouts" at 5:30 (PT)/8:30 (ET), while Los Angeles saw it on "fast kine" three hours later (or someone at the station made the kinescope during the live feed).
Somebody mentioned the practice of welcoming new stations to a broadcast; sometimes that was the biggest news of the day, and the networks (particularly ABC) wanted to promote their steady expansion. I still remember Aug. 1, 1962, the day WRAL switched from NBC to ABC and became the second fulltime ABC affiliate in North Carolina (after WLOS); it was mentioned on three daytime shows, "Yours For A Song" with Bert Parks, "Camouflage" with Don Morrow, and "American Bandstand," all of which were live. And even when ABC began picking off other networks' affiliates in the '70s and '80s, the practice continued; I remember the morning in 1990 when WHAS Louisville joined ABC and Charlie Gibson acted delighted that one of the oldest and most prestigious stations in the country had moved from CBS to ABC.
It's still probably a hassle to switch football games; CBS went to bonus coverage of the Browns-Titans game yesterday, but both WCBS and KCBS had to cut away by NFL rules to show the Jets-Chargers game in its entirety. WFMY and WRAL, my local CBS affiliates, stayed with the Browns-Titans game to the end.
But this discussion is otherwise getting too technical for me; all I know is that the first live network broadcast we got in North Carolina came in 1950, before I was born; WFMY carried DuMont's telecast of the North Carolina-Notre Dame football game on the day live network programming was extended southward from Richmond at least to Birmingham. I do have some insight now as to how, if in the '50s I had worked at a station that carried both Jackie Gleason (CBS) and Sid Caesar (NBC) on Saturday nights, I could have switched from CBS to NBC at 9, when Gleason went off and Caesar came on, to use one example (or in the '60s, how CBS/ABC affiliate WMAZ Macon, GA could go directly from Gleason to Lawrence Welk (ABC) at 8:30).