From my observations it's genetic. Just like people have different hair color, eye color, height, etc. I'm a morning person. I function well on 7.5hrs sleep. Wi

From my observations it's genetic. Just like people have different hair color, eye color, height, etc. I'm a morning person. I function well on 7.5hrs sleep. Within reason I can go to bed anytime and wake up less than 8hrs later. My wife is the typical owl. She sleeps till 10 and is barely functioning even after coffee until the early afternoon. In my experience, it is easier to not fight your natural circadian cycle. Just organize your day to match your changing aptitudes.