A solution to this problem may be a dynamic penalty based on the reason why you are leaving.
The Problem we have here is "more work for GMs".
You can leave anytme you like but you need to give a reason in a text box.
A GM will check and give a penalty of 5 minutes up to 3 hours...
An other problem is the reaction time of GMs, they need to check and that way you may wait in GM prison 5 minutes or longer before coming back to the real world