I did it several different times, between 6 pm and 11 pm, and there was always available washers and driers. You should be fine anytime. I would think that when people are still at parks would be the best. We were in the 1950s.
I usually do any laundry after dinnertime...no matter where I'm staying that seems to be a good time...usually around 9ish. Or very early in the morning.