Or go into system programming, night service, group assign, put in your operator extension number, and then assign a number associated with the phone you want to ring at night.
Put a night service button on the console, and when pressed it will make calls to the operator ring at the "night" station. The main advantages of this are pressing a button turns on / off, and that you can have ALL the rest of the phones ring if need be. Downside is if you have automated attendant service controlled by your attendant state, pressing the button at 10 in the morning would cause your AA to answer with the closed message.