At night, I typically go into the "zone" where I'll allocate most of my attention span to my code base and to the syntax of a particular language and to the higher-level problem at hand, and my productivity is pretty high. But during the day, I usually can't get into that state, so I bounce back and forth between talking to people, answering questions, meetings, and coding.
You can say the same of very early morning. With the added bonus that then your brain is refreshed and works faster.
Ie my most productive coding sprees are from about midnight through 10am. And then I hit a brick wall ;)