I was looking at a couple of Hansard reports and noticed that the last House of Commons debate of the day was preceded by a motion to adjourn. If the debate lasted more than half an hour, it was cut short. You can see examples of this at 2020-06-04 (not cut short), 1993-06-17 (cut short mid-sentence), and 1993-06-18 (cut short mid-sentence).
My question is why do it that way. If the house wants to adjourn, why not adjourn immediately? If it wants another debate, why not move to adjourn afterward, and then adjourn immediately? I assume there's some parliamentary reason behind this "let's adjourn now, effective in half an hour", but can someone explain it to me, please?