I'm usually most productive from 2am to whenever I fall asleep, which has been somewhere between 10am and noon as of late. Great sleeping cycle, I know :) It's almost impossible to get anything done during the day, especially on a college campus - so many distractions!
For me the hour depends on how excited I am about the project i'm working on, could be night, morning, doesn't matter.
However my best ideas happen at night.
strange you ask, but i guess just like most will admit here, productivity is at peak for me in the cold hours of the night. It's like darkness brings with it some aura of heightened awareness and gravitation to creative work - code at least.