Talvez tente Sleepwatcher . Não posso garantir, mas achei depois de seguir as dicas do Kevin:
SleepWatcher 2.0.5 (now compatible with Mac OS X 10.5 “Leopard”) is a command line tool (daemon) for Mac OS X that monitors sleep, wakeup and idleness of a Mac. It can be used to execute a Unix command when the Mac or the display of the Mac goes to sleep mode or wakes up or after a given time without user interaction. It also can send the Mac to sleep mode or retrieve the time since last user activity.