Starting September 1, Pandora's 40-hour limit on mobile devices comes to an end, which means you can now choose to fall asleep to Pandora at night without worrying about a limit. However, if you're not one of the lucky few who still have an unlimited data plan on your mobile device, you probably don't want Pandora streaming all night long, eating away the precious data on your tiered plan and sucking your battery dry before your morning alarm goes off.
In response to customer suggestions, Pandora has finally added a sleep timer to its mobile apps (iOS | Android). To enable the sleep timer, start listening to a station, then go to Menu. Tap on "Sleep timer" to bring up the three timer choices: 15, 30, and 60 minutes. Once you select a time, the countdown will begin. If you change your mind, you can tap on the countdown to cancel it.