Somewhere between 8pm and five am has always seemed to be my optimum writing time. I often wonder these days if it's half the reason I have so much trouble keeping up with things: 8 -midnight most nights tends to clash with my irc conversations.
After several storming hours of non-stop, high-speed writing on Masques at the tail-end of last year, when I did a few stints of starting at 8pm and just not stopping (literally!) until five am, it took me so long to get my sleep patterns back under control and normal again that I don't think I'll risk that one again any time soon!
Although, have to say, sometimes I'm sorely tempted.
LabRat