When I go camping my body almost immediately reverts to a more primitive cycle of waking up immediately at dawn and going to sleep at sunset. Takes about 3-4 days.

It's just so much better psychologically and physiologically but it's also amazingly practical. I don't need a flashlight and the BEST time to hike and be active is dawn and dusk when it's cooler.

I'll even start taking naps in the middle of the day the same way other large animals do (bears, deer, etc).