I've never been a morning person. The daily grind forced me into at least minimally functioning in the morning.
When I've been out of work, I tend to become a night person. That's not to say I'm out partying or anything like that; it's just that I tend to function better at night.
Or at least that's the way it was when I was younger. Nowadays I'm usually passed out on the sofa shortly after dinner and in bed for realz between 10 and 11 pm, even on the weekends.
However, if I'm actively engaged in something, I can easily stay up well past midnight and remain fully awake.
Of course, even if I go to bed at 2, I'm still wide awake at 6:30 am…another lovely byproduct of getting older.