Then you have to use RCON (if the game supports it) and make it dependent if someone is connected that a message is sent to the users that the server is restarted in n minutes and after that restart it.
Okay, then I can't help with that, maybe make a request for such on app an the Plugin Support forums.
Maybe someone is willing to create such a thing.
I have to also say that I really don't recommend that users can start/stop servers, can be very bad sometimes...