I usually get up at least once a night to use the restroom, so I always fall back asleep. So I dont necessarily have the problem where I cannot fall back asleep after I wake up in the middle of the night. As far as the different bed times, it varies on the weekend. As long as I get 3 or more hours of sleep, it really shouldn't make a HUGE difference. I dont think charts are ever going to be 100% accurate, because things can happen during the course of your cycle. Plus, you want to look at the overall pattern on your chart, not just one day. Although, I can be a hypocrite on that one...because I get excited when my temp drops (O time) or my temp shoots up (post O).