The 11:00 local news was the only way to find out who won a ballgame that night (without actually watching the game) and to find out what the weather would be the next day (well, 50/50 chance of them being right about that).
At 11:30, most people would switch over to Johnny if just to catch the monologue, as I did. The monologues were usually razor sharp. His guests were mostly boring if I recall. Tony Randall seemed to be a guest every other week. Then you had people doing magic tricks, dogs running through hula hoops, the general late-night mayhem.
Young David Letterman had a late-late night show for the real insomniacs. He was actually cutting edge back in the day, before he turned into a totally nasty person both on and off stage. Johnny Carson however was classy to the end.
I could never understand why both coasts run their local news at 11:00, while for “flyover country” it’s always been at 10:00.