[old_tv_nut]

Actually, networks grew rather quickly. First run prime-time programs on film could be televised multiple times a night at the network head and sent over the network to the different time zones. Live shows, however, could not be played multiple times until video tape became available. Once tape was available for first run, the tape was played multiple times at the network source and sent via the network to different time zones, just like film.

Before video tape was available to the networks, first-run live programs were recorded and delayed by kinescope recording (a film camera imaging a picture tube), at first in black and white, and then, for a period of about a year and a half, NBC used color kinescope recordings; that was replaced by video tape. All of these techniques were used to record and playback at a central network location, except for a few special cases like Alaska, who had no network connection.

Time zone delay was usually set up so that the first presentation was simultaneous in the Eastern and Central zones, then the delayed transmissions were made to Mountain and Pacific zones. Hence the typical announcement "Watch {x} at ten o'clock, nine Central."
People who haven't lived in the Central time zone may not realize that many businesses (not all) in the Central zone shift their hours to match typical starting times in the Eastern zone. The prime-time TV schedule being shifted also meant that local news typically at 11pm in New York would go on at 10pm in Chicago.

After the first run of a program, the networks would license them to syndicators for reruns, who in turn would license use to local stations, often as 16mm film. The local station could run 16mm locally at the time it chose, whereas the original network run would likely have been 35mm and would have been in lock step with the network schedule.

Local stations also had access to syndicated old movies (generally as 16mm copies, although some large stations had 35mm capability), until Ted Turner and others realized that much more money could be made by putting old movies on cable pay TV.

By the way, as has been discussed in other threads, the 16mm film was acetate "safety" film and did not require special fireproof facilities that were needed to handle the 35mm nitrate movie film.