As a "reaching out" eighteen year old in the late 1970's I occasionally ran the sound desk and I had an assistant to put the roving microphones away and make sure the record player needle was lifted on and off carefully so as to not scratch the kingdom songs record while I switched it off and switched on the speaker's microphone for the closing prayer.
We used to time the prayers (and place a non monetary bet with each other as to what the time would be - the closest got bought a pint of beer by the other at the pub afterwards) with the stop watch used for the student talks. The longest was 7 minutes 11 seconds.
I bet 5 minutes 5 seconds and my mate reckoned 5 minutes 20. He was closest and got bought the beer!