What time should I go to bed if I wake up at 5:15 pm?

For a 5:15 pm alarm the day is your night. Five cycles start at 9:30 am; the minimum four start at 11:00 am.

Why three times and not one

The middle option, 9:30 am, is five cycles and 7 h 30 min of actual sleep; 8:00 am is six cycles and 9 h. Both sit inside the adult range. The 11:00 am option is 6 h: enough to get through the day, not enough to do it twice.

A cycle is one trip through light sleep, deep sleep and REM. The 90-minute figure is an average from NIH material; your own cycles could run 70 to 120 minutes, so treat each time as the middle of a 15-minute window.

Walk through the night from a 9:30 am lights-out: asleep by about 9:45 am, into the first stretch of deep sleep around 10:05 am, first REM period near 11:00 am, the halfway point of the night at 1:30 pm, and the longest REM period of the night starting around 4:40 pm — which is what a 5:15 pm alarm at the end of cycle 5 lets you finish.

All bedtimes for a 5:15 pm alarm

Formula: bedtime = wake time − (cycles × 90 min) − 15 min · adult range from the NSF 2015 panel and the AASM/SRS 2015 consensus · methodology

If you can't fall asleep by 9:30 am

Fifteen minutes is the average time a healthy sleeper takes to drop off; ten to twenty is normal. If you are still awake twenty minutes after 9:30 am, sleep-medicine guidance is to get up, do something dull in dim light, and return when sleepy — lying there teaches the brain that bed is for being awake. Miss the window and the next one, 11:00 am, is only a cycle away.

Try a different time