Are you a morning person or a night owl?
When I was young, I was sooo much of a morning person. Even on a few hours sleep, I felt great. Now, I need at least 7 hours sleep to feel great the next morning. Predicated on that, I feel great in the morning!
All too often I stay up way later than I should. I can stay up 20 hours and totally throw off my normal sleep schedule. Staying up late is reserved for the weekend.