It's not so much about when you work, but that you have a set schedule and routine. If you have a job, usually this is during the day. Knowing when you wake up every day that you will be working at these exact times tremendously helps your focus and production.

Very often late night, sporadic sessions are a product of, "oh crap I have to get some work done! Time for coffee and pounding out as much code as I can."

Not saying you can't be productive at night, but real production comes from day in, day out routine and dedication to the work. It's not as sexy but it's the reality of the job.