When I started writing, I almost always began writing at around 10 or 11 PM, and then I'd write until about 2-3. Eventually, I realized that this was not efficient. My energy levels at night weren't the best. And, moreover, there was too great a chance of something coming up. Basically, I was finding myself in situations where I had to choose between going out and doing my day's writing, and I didn't want to live the kind of life where I always needed to be at home at 10 PM. So I started writing during the evenings.
Except even that was inconvenient. I get tired during the evenings. I want to nap. And people want to do stuff! They want to go out for evening drinks, dinner, etc. So during graduate school I established a policy that I would always get my day's writing done by 5 PM. It's a great policy, and it's a huge relief. Sometimes during the evenings I'll be lounging around, not doing much, and I'll think, Oh my god, shouldn't I be writing? And the answer is no! It's after 5 PM. I don't write after 5 PM.
So for about the past two years, I've been starting my writing day at around 11 AM or so, and writing for 1-4 hours. Which has worked fine. It leads to long, leisurely mornings (since I tend to wake up at 7-8 AM), where I do a lot of internet stuff and a lot of reading. Sometimes I'll read for two hours before I even get out of bed.
The problem, though, is that my morning hours are my best hours. Oftentimes when I wake up, I just feel so bright and happy and excited to tackle life, and then by eleven o'clock that feeling is starting to fade, and by 1 PM it's completely gone.
So for a long time I've thought that maybe the thing to do is to start writing shortly after I wake up, and then to write for however long, and then leave the afternoon hours to more low-energy activities (reading, blog-writing, freelance work).
It's too early to say if this is a good idea, but I've been starting work at 9 AM for a few days now, and so far it's excellent! Just really, really game-changing. I start work feeling very fresh, and if I decide to quit work at 12:30 (as I did today), I've still done a more than average day of work. It honestly feels like I've gained two hours in the day. I think that's because my morning hours, although the reading was good, were fundamentally procrastination. I haven't actually been reading less--I've just displaced the reading into the evening.
Still haven't figured out the best time for blog writing, though. I keep having to do it at midnight.