The need for sleep varies like most biological functions, but you can fit the differences among virtually all adults in about an hour's span. It's likely that people who, in casual conversation, say they're fine on four or five hours a night have been acculturated to not value sleep or what sleep does for them. Or they're supplementing their waking activity with stimulants such as caffeine and nicotine. People are not good at perceiving their own sleep debt. There's a new clarity in how they perceive the world.
School administrators say all tenth-graders have to do is go to bed an hour earlier.
They end up losing sleep. You see this problem in universities and high schools and even some junior high schools. Little kids are still protected by an ethic that young children need sleep, although some parents seem to be keeping their kids up later to get quality time with them after work, then waking them up earlier to get them to preschool or day care. We need a heightened awareness that sleep affects us, as does the lack of sleep, and that our ability to function is impaired during certain times of the day. At the same time, we can't turn back the clock.