Check out what is likely the most illuminating interview with Henry of them all, his chat with the Paris Review from 1962, just as he was attaining elder statesman status here in his homeland.
For example, when asked “Are there certain times of day, certain days when you work better than others?” he responds:
“I prefer the morning now, and just for two or three hours. In the beginning I used to work after midnight until dawn, but that was in the very beginning.
“Even after I got to Paris I found it was much better working in the morning. But then I used to work long hours. I’d work in the morning, take a nap after lunch, get up and write again, sometimes write until midnight.”