You wake at two in the morning. Your mind is clear. The house is quiet. And instead of using it, you spend the next hour calculating how much sleep you'll lose if you don't get back to bed right now. What if that hour wasn't the problem?Most productivity advice is built for one type of person—the early riser, the disciplined morning worker, the one who wins the day before seven a.m. But chronobiology tells a different story. Every person has a natural productivity window: a specifi...