That sounds a bit convoluted, so let me try and explain: in 1975, the FCC created the "Family Viewing Hour," mandating that networks had to schedule family-friendly programming (without too much sex or violence or other interesting stuff) between 8 and 9. The Family Hour was struck down by the courts in 1977, but even after that, there remained a perception -- which lasted for many years -- that the 8 p.m. hour was for family programming and that anything that was primarily aimed at adults should be scheduled after 9.
You can spot the change if you pick up the Complete Directory to Prime Time Network TV Shows and look at the scheduling of All in the Family. In the early '70s, it was usually on at 8 p.m. With the coming of the Family Hour, it was moved to 9 p.m. In 1978, after the repeal of the Family Hour, the show was moved back to 8 p.m. -- but when it was, a little girl was added to the cast. It was pretty much a given that a show that aired at 8 or 8:30 had to have a kid, or at least something to appeal to kids. Gone were the days when the original, adults-only All in the Family, or M*A*S*H, could air early in the night.
Some shows, like AitF, were re-tooled to fit the new demands of the early hour. Others just had to tone themselves down to the point of blandness; an often-cited example is Susan Harris's first show (first one she created, I mean), Fay starring Lee Grant. It was scheduled at 8 p.m. in 1975, so Harris couldn't do much of her trademark sexually-frank humor, and the show was never as good as it might have been (Harris finally got to show what she could do with the 9 p.m. show Soap). There must have been other shows that were forced to tone down the jokes, or add an unnecessary kid or something, just because they were airing before 9.
Then there were shows that were scheduled at 8 despite having little or no kid appeal, and suffered for it. The example I like to bring up is my beloved WKRP in Cincinnati. Everybody knows that CBS constantly changed WKRP's time slot, but that wasn't actually the worst thing about the way the show was scheduled. The problem was that except for the few months when it was airing at 9:30 after M*A*S*H, CBS constantly scheduled it in the de facto family hour. Look at the time slots it had (not counting its many different summer-only time slots):
Sept. '78-Nov.78 Mon 8:00
Jan. 79-Dec. 79 Mon 9:30
Dec 79-Jul 80 Mon 8:00
Nov 80-May 81 Sat 8:00
Oct. 81-Jan. 82 Wed 8:30
Jan 82-Feb. 82 Wed 8:00
Mar. 82- Apr. 82 Wed 9:00
The only time WKRP was considered a hit was in 1979, when it was airing after M*A*S*H. But the problem wasn't just that CBS moved it out of the cushy time slot, but that they kept scheduling it at 8:00 when shows were expected to have kid appeal. The perception at the network was that it had kid appeal because of the rock music, but it was a mistake; there were no kids on the show, not even any teenagers, and it needed a "grown-up" time slot like the other MTM sitcoms had gotten. But CBS didn't move the show back to 9 until the very last month of itss run.
There's no question that WKRP would have become a long-running hit if it had been consistently scheduled after 9; that was when it thrived and that's where its audience was. That's the example I know best -- but there must have been other shows that got killed by being placed in the Family Hour when they didn't have Family appeal. Hence the need to go through the Directory to TV Shows and make a list of shows that might have lasted longer if they'd been on an hour later.