Well, suppose I need to get up at 07:30. It advises me to go to sleep at 22:30, which is 9 hours, or 6 cycles. If I'm out by just 10 minutes, that's an hour.

Well, suppose I need to get up at 07:30. It advises me to go to sleep at 22:30, which is 9 hours, or 6 cycles. If I'm out by just 10 minutes, that's an hour. So perhaps I should go to sleep at 21:30. Or at 23:30. There's a big difference. I do love the idea - the challenge it trying to work out whether I'm average. 8-)