"My circadian rhythms are set for late nights," writes mysillyvalley.
After years of experimentation, I have figured out that I'm most productive between 4 AM and noon. Because I have few interruptions before 6, the hours between 4 and 6 AM are super productive for me, if I'm awake. When I was in college, I used to try to get access to those hours "the hard way," by staying up late. Now that I'm a grown up person and somebody's Dad, I get up early in the morning. These days, it's not unusual for me to wake up around 4 and stay up.