The local mup near us is scenic, with 4 parks which connect, each with different characteristics. I usually ride them only during the week, and during hours when people are usually working. Guess I'm lucky as the heat doesn't bother me as much as it does some. I led a ride of 5 the other day, and people were commenting on how hot it had gotten. Was a 20 mile ride, felt like I could easily have done another 10 or so, even with the heat. Guess it depends down to how heat tolerant you are, as to when you're most likely to get a ride in.