It has been a long time since I have approached 4:00 am from nighttime end ("wow, I really should be sleeping, I have to get up so soon..."). I am up at 4:00 am fairly frequently on the "crap it's still dark and I have to get up" end of things.
However, this week I did see 4:00 am--because of a severe case of NII (Novel Induced Insomnia). Yep, could not put the darn thing down. The Farseer Trilogy, by Robin Hobb if you were wondering.