RTE 1 used to have an interlude every weekday for years at 1.30pm for about 10 minutes. This was after they started a 1.00 News Bulletin around 1989. Eventually, someone had the bright Idea to show Aertel Financial pages after a year or so in the gap.
It was also not unusual for them to start up some days in the 80's and then announce that programmes wouldn't be starting for another 10 or 15 minutes. Obviously, they would have a legitimate excuse when it was a live event, but occasionally this wasn't the case.
I remember the days of BBC TV menu interludes. Mainly seemed to be at startup after Pages from Ceefax and before the first programme of the day. Example of a Saturday menu startup from 1991 here:
Also of course there were interludes between schools programmes on both BBC and C4 where we heard these classics!
We are currently discussing these (in passing) in the Breakdowns thread, but Channel Four’s break-fillers between 1982-1992 could be quite elaborate, which is surprising in a way because in theory these were only a sustaining feed which, if sufficient ads were sold by the regions, viewers would never see!