What does 'it was a lot of airtime to fill' mean?

Hello everyone. Can you please make that sentence fragment more clear? I don't understand what the author want to say.

Generally speaking, each network ran three hours of primetime programming from 8pm-11pm Monday-Saturday, and four hours from 7pm-11pm on Sunday. The 10pm slot was typically occupied by detective shows or soap operas, and the 7pm Sunday slot was reserved for public affairs programs, which meant that half-hour comedies almost always ran between 8pm and 10pm. That’s eighty-four potential shows, and while not every network broadcast comedy every night, it was a lot of airtime to fill. Family sitcoms were the bricks and mortar of the network television house.