Glenn Howerton believes that humans sleep in 90-minute cycles and that sleep duration should align with those cycles.

“what so what I've heard and I don't know if you guys have heard this but that our body sleeps in 90-minute Cycles right so you want to you want to be on a 90-minute cycle no matter what it is whether it's hour six you wake up six hours of sleep that's 90 minute cycle seven and a half that's 90 minut”

The brain cycles through non-REM and REM sleep every 90 minutes, with the first half of the night favoring deep non-REM sleep and the second half favoring REM sleep.

“in the first half of the night the majority of your 90-minute sleep cycles are comprised of lots of deep non REM sleep and very little REM sleep but as you push through to the second half of the night now the seesaw balance changes and the majority of those sleep cycles are comprised much more of ra”