If I'm trying to get a certain distance in a day, I start right after the sun starts lightening the sky. If I'm close enough to a town, and not trying to hurry, I wait for the sun to fully rise. That helps a lot, with being seen. 👍
A lot of the time, I end up riding right through the day, but with several short breaks. Like Robbie, I seem to ride better in the heat. For me, I think that's when my arthritic old knees feel best, nice & warm. 😎