This website has more info.

Basically try to sleep 6 or 7.5 hrs each night. I guess try to imagine it like water. The surface is when you’re awake. Stage 1 (N1) is like a couple feet under. Stage 2 (N2) is maybe 5. When you go down to say like 15 feet, you’re in deep sleep (N3), REM (Stage 4) is like 10 feet (it’s closer to the surface because brain activity is higher as this is when you’re dreaming). Then you start going back up to the surface and you start again, this takes on average 90 minutes. You want to wake up when you’re just under the surface and you go through 4-6 cycles a night. Now everyone is different and different lengths to their sleep cycle so try 6 hours, then 6.5 hours, then 7 hours, etc. and when you don’t wake up groggy, then try to stick to that length of time.

I think there is an alarm clock that simulates the rising sun according to when you want to wake up so it will naturally help you reach Stage 1 and you won’t feel groggy.

Also, it’s better if you sleep when there’s absolutely no light in the room and it’s colder. Blackout blinds are a godsend.

Hope this helps!