I wonder if there's an age component. I read that same book and I remember (maybe erroneously) that the artists who worked best in the morning were older, whereas the artists who worked better at night were younger and oftentimes addicted to stimulants.

That more or less describes my working patterns over time, too, including the addicted to stimulants part. When I was young, my most productive time of day was after everybody fell asleep. Now, it's before everybody wakes up.