I've been told our bodies have a natural rhythm of sleep and wakefulness influenced by the sun (or its absence in the sky). Generally, sleepy when it's dark, wakey-wakey when it's light.
It's never quite worked for me the way they say it should.
My inclination is definitely to be a night owl. I could happily stay up until the wee hours of the morning. I do a lot (but not all) of my writing later in the day and into the night. That makes my choice of day-job problematic—primarily because it happens during the day. I love teaching, though, and I love the age levels I work with. (Yeah, teaching afternoon/evening classes at a college could solve the problem, but it's not what I want to do right now.)
So, I find myself living a hybrid life. During the school year, I force myself to follow a reasonable sleep schedule, although I'll push it a little on weekends. Then during summer break, I'll shift more to night-owl mode.
This works out pretty well most of the time, but it causes problems at this time of year—when I have to readjust myself back to school-mode.
At least this year I don't have to commute.