Within System Preferences > Energy Saver, there are all sorts of useful settings to tweak. You can configure how your Mac’s sleep behavior functions (both when you’re using the battery and when it’s plugged in, for you laptop users), and in Lion, you can also tell your machine to automatically restart if it freezes completely. In this tip, though, we’ll cover how to schedule automatic startups and shutdowns. It’s pretty neat to have your Mac all up and ready to go for you when you sit down with your morning cup of coffee.
So first, unlock the pane by clicking on the lock in the lower-left corner and entering an administrator’s name and password. Then choose the “Schedule” button to set up your Mac’s behavior.
As you can see above, you have a few options. Set your computer to start up or wake at a certain time on a certain day (or you can configure it to do so on weekdays or weekends, for example). You can also ask it to sleep, restart, or shut down on the schedule you choose.
There are a couple of caveats here. First, if you’re on a laptop, your machine won’t follow the rules you set for startup if it’s not plugged in to power. Note, too, that if you’re logged out of your account or if your machine is asleep, it’ll ignore the command to shut down. Aside from those things, though, your Mac should do what you ask of it. Until it becomes self-aware in a few years, at least. What? Haven’t you seen The Matrix?