Sleep timing
Sleep runs in cycles of about 90 minutes. Waking at the end of one tends to feel easier.
Assumes about 15 minutes to fall asleep. Adults generally need 7-9 hours. This is a planning aid, not a diagnosis; persistent sleep problems deserve a conversation with a doctor.
Method: sleep cycles of roughly 90 minutes with about 15 minutes to fall asleep. Cycle length varies between people and nights, so treat results as a starting point.