@ER3017- Thanks for the info from the schedule. With a two-hour feature (The Court-Martial of Billy Mitchell) including a few commercial spots in between, it does take up a lot of time to force a station like WBBM-TV to cancel the sermonette.
CBS O&O's were notorious for their Late Show lineups circa 1979-1980 IMHO. In places like NYC, Philly and Chicago, it was most common. But in LA, it was variable and in St. Louis, schedules were "normal:" between 1 and 3 in the morning, especially on Sundays.