FAQ
Why 90 minutes?
A complete sleep cycle (light → deep → REM → light) lasts roughly 90 minutes for most adults. Waking up at the end of one feels much better than being jolted out of deep sleep.
How many cycles should I aim for?
Five to six cycles per night (7.5 – 9 hours total) is ideal for most adults. Four cycles (6 hours) works in a pinch.