Sleepy Clock is a sleep cycle calculator for your Windows Phone. What is a sleep cycle calculator you ask?
A sleep cycle is 90 minutes long and in general, you need 5-6 cycles to be well rested. Sleepy Clock goes about calculating the amount of sleep you need to be well rested from two approaches.
First, you can enter the time you need to wake up and Sleepy Clock will show you a range of times you should try to fall asleep at to get enough rest. Next, if you are about to fall asleep you can see a range of times you'll need to wake up at to be well rested.