It took me awhile but I think I got it down.
For example: Say When! aired in a 25-minute time slot with 21 minutes devoted to the show itself, followed by the NBC news. But it was even worse when Celebrity Whew! (which preceded the CBS News) aired on CBS as only 18 minutes were actually devoted to the show itself due to increased commercial time over the two periods.
Truth is, I'm only familiar with duration of primetime network programming. Back in the 50s, it was 26 minutes (w/o commercials); 25 minutes in the 60s and at least most of the 70s, 24 minutes in the 80s (sometimes 23 minutes), 23 minutes in the 90s, (sometimes 22 minutes) and so on, and so on.