I don't know if I'd call it "the presenter has messed up their back timing" but rather the hour was short due to scheduled music and spots not timing out for any number of reasons. We had a list of fill songs to use for that exact occasion. Nowadays flex scheduling allows stations on autopilot to add/drop predetermined categories as the hour goes, but it used to be the last song of our hour was a drop song if we were over, and we had a list to rotate through if we were under. But it was hardly because anyone "messed up"Roll to Me by Del Amitri is famously just over two minutes long and frequently heard right at the tail end of hours on radio stations where the presenter has messed up their back timing and needs to hit the TOTH.