Any time is best. I've been known to leap out of bed at 5:30 because I figured out a quilting design dilemna in my sleep. I've also been known to prod myself to do one more block or join one more row at 10:00 p.m. On the weekends, I'll be in and out of the sewing room all day.
But the routine that I am in right now is about an hour in the morning and an hour or two after dinner.