Those are funny conventions I never thought about. Humans try to guess what the other person says. I wonder what the interval is of that.

Besides the obvious (perceived complexity and potential cost/benefit of the topic) I think the pitch of someones voice is a good indicator if they want to continue their turn.

It depends a lot on the person of course. If someone continues their turn 2 seconds after the last sentence they are very likely to do that again.

The hardest part [i imagine] is to give the speaker a sense of someone listening to them.