The time limit should be set so that even if you think carefully, you still have a little time left. In this case, the timer will be a motivation to make your move quickly – not everyone has the time or desire to wait for excessively long turns.
Otherwise, there will be no such motivation; what's the point of having a timer at all? Just agree on an unlimited time and take as long as you need for your turns.
I didn't quite understand the meaning of the last sentence... I'm saying that I prefer 10 minutes not to deliberately prolong my turns and wear down my opponent, but to have some leeway, so that when I need to think, I have time, and I don't have to do everything in a rush... and if everything is done quickly during a turn, then the turn will be passed earlier – I don't remember ever having the habit of taking 5 minutes for a turn and then just waiting for the game to pass the turn to my opponent after the time has expired...