you can run Hamachi 24-7, but it seems the server will not work right for a map or two if it sits idle for many hours. Not a big deal. You obviously run the normal in-game dedicated server mode, not the old command line gamespy-only server.
Bigger problem is to find players who have your Hamachi info installed and actually show up to play. If you have that, you can play for as long as you're paying your Hamachi account bill.