The duration and timing of sleep impact the type of sleep obtained, with different sleep timings leading to selective deprivation of deep sleep or REM sleep.

“So it really just means that the, your profile of mental and physical dysfunction will be different under both of those conditions. Which one would you prefer? I would prefer neither of them.”

“the type of sleep that you get will not be the same you will be selectively shortchanging yourself of sleep either of deep sleep or of REM sleep on either side of that equation”

“So when I'm saying the optimal position of sleep, I'm saying with the optimal for your chronotype, this is your chronotype...And by the way, it's genetic. You don't get to decide whether you're a morning type or an evening type. It's hardwired into your genes. We know the genes. It's not your fault. If you're an evening type and you're listening to this, and society, which is strongly architected against your chronotype, we reward and we favor the morning types, it is not your fault. It's not a choice. And there's not too much you can do about it. You can push and pull the system by about 30 minutes, 45 minutes, but not much more. So coming back to it, when we position that sleep on that eight-hour period, whatever is optimal for you, you will get a nice distribution. You'll get all of the deep sleep that you want and all of the REM sleep that you want.”