I've found the free Sleep Cycle[0] app to be very useful visualizing my sleep patterns, plus it lets you set a 30' window (free version; perhaps other options in the paid version) for waking at a near-waking point naturally.

[0] https://play.google.com/store/apps/details?id=com.northcube....

or

https://itunes.apple.com/us/app/sleep-cycle-alarm-clock/id32...