I think a lot of us do that and after awhile I started taking note of the amount of time I was asleep before waking so alert and ready to go. Now I set my alarms to coincide with that. For me it's about 3.5 hours so I have one alarm that wakes me at 2:30am than another for 7am. Seems to work for me though my wife and friends say I'm crazy for waking myself up in the middle of the night. But for me there's that calming realization I have nearly 4 more hours of sleep before waking up for good. Makes those last few hours even more precious.