I find that I rarely eat the moment I get hungry. For breakfast, I force down a bowl of cereal. For lunch, I am watching the clock for a good half hour before, my stomach pinging me. And then there's the occasional random case where I am starving even though I know I'm not hungry, or feeling full until I eat the first mouthful.
If I ate the moment I felt hungry, and no other time, I'd eat at very different times.
Same with sleeping - I go to bed at the same time each night, +/- an hour, because I know that if I don't I'm not going to sleep well. Too early, I wake up at an odd hour. Too late, I'm tired. My tiredness has little to do with it.
My brain dictates the schedule, my body just has to deal with it. Were my body dictating the schedule, my brain would not be thrilled.