It’s always been possible to sleep or even wake-up a Mac on schedule via the Energy Saver pane of System Preferences – just click the Schedule button at the bottom.
However, for a truly easy-to-use scheduler you can use Sleep Timer App, which is free. This lets you click a menubar icon to set a time period after which your Mac will go to sleep – ideal if you like to watch movies late at night, or listen to music.
You can set a period of 15, 30, 45 or 60 minutes and when the timer is up a notification appears that lets you delay the sleep for another 10, 15 or 30 minutes. If you choose not to respond to the notification, or are unable to do because you’re asleep, then the Mac will sleep after one further minute.
In short, if you tend to fall asleep while using your Mac then Sleep Timer App is the perfect solution.