For takeoff and landing we usually like the crews to be the ones who had the most recent nap, but really, beyond that, avoiding the window of circadian low, if possible, before takeoff and landing is a good idea.
If you look at pilots over the long haul—three days prior to an international flight, during the flight, on the layover, on the return, and then back at home again for three days, so a nine- or ten-day period of time—what you see is that there is really only one night typically out of those nine or 10 nights where there is significant sleep loss.
Most people—