Not sure why you'd want to know this, but...
My day/night cycle is unpredictable at best, and I don't recommend it as something for most people. My days cycle is generally 28 hours long, so I only sleep 6 times per week. I usually work for 19 hours then sleep for 9, but that's not a rule. I simply go to sleep when I'm tired and can't focus anymore. This regime has yielded the most productive results for me as I've discovered, with approximately 15 hours of productive work done each day. Whenever I fall back onto a "normal" sleeping schedule (happens after trips, vacations, scheduled appointments etc), my productivity plummets down to 3-4 hours per day.
Today I woke up at 11:30 PM for example. How my wife puts up with me is a mystery.
I generally prefer to do NGUI support the first thing in the "morning" -- this can take anywhere from an hour to 6 hours, depending on how recently the last release was. If there are issues to investigate, it takes longer. Once that's done, I move on to other tasks -- be it improvements for NGUI, prototyping something random, or -- more recently -- game dev. Whatever I start with at the beginning of my day is most usually what I will remain focused on for the rest of the day.
Sometimes this can be a bad thing. For example I spent all of yesterday playing Kerbal Space Program trying to land on Minimus and get back safely. I succeeded after about 5 hours, but kept playing the game for the rest of the day in attempt to create a more efficient design for an inter-planetary rocket.
Other times it can be a very good thing. The entire layout system redesign and implementation for NGUI 3.0.7 only took me ~2.5 days, as an example. If I was to estimate it now, I'd say it would have been ~3 weeks worth of work.
The odd sleeping schedule and hours aside, the one suggestion I can make that works for just about everyone is to stay on track doing what you're doing if you feel that you are being productive -- and for as long as you can. And when you're not -- well, go do something else. Watch Netflix, play something, or just get some sleep. It's not easy to manage with a 9-5 job, but if you can set your own work hours, I would strongly advise it.
