Apple really ramped up its health efforts a few iOS versions ago and one of the sleeper hits (pun intended) is the bedtime feature.

Buried in the clock app on iOS is a tab called bedtime. In here you can set your wake up time (this also sets an alarm) and how long you want to sleep. Once you do this, you get a bedtime reminder every night and sleep data populated into your Health app. If you set the option your phone will also turn on Do Not Disturb mode during your sleep.