Jonnyg: Andrew's answer is the only way to do what you asked for. Kabster's method uses a timer, that is setup in advanced (like he said, he has one for 2:30 and one for 3:30 running every day) there is no button to push.
A third idea that I was toying with when I was creating my ProntoPro
CCF is to create a timer (sleep) panel with many timers setup for different times, but no days. Then when you need the sleep timer you just pick the button in edit mode and click on the time. To be able to edit timers, they must be on the macro side, and the buttons cannot contain anything else