I'm not sure how much it's going to help riding 200km rides. We 2 back to back in 2019 and it's pretty easy even though it was really hot. The second day it got to 100F pretty early on. The second day after riding 400km + is a whole different experience. I generally feel pretty awful until about 5pm. But the first 15km can feel impossible. After 500k, it's easy.
Sleeping the day of a night start definitely helps. Evening start PBP riders from the U.S. shouldn't try to change their sleep cycle too much before the start, because early evening French time is when we usually start our rides. It's really easy to waste energy before the start at PBP. Go sit in the courtyard or the food tent.