What time should I go to bed if I wake up at 4:00 pm?

A 4:00 pm wake-up means sleeping through the morning: lights out at 8:15 am for 7 hours 30 minutes.

Why three times and not one

The middle option, 8:15 am, is five cycles and 7 h 30 min of actual sleep; 6:45 am is six cycles and 9 h. Both sit inside the adult range. The 9:45 am option is 6 h: enough to get through the day, not enough to do it twice.

Why cycles at all? Because what you wake from matters more than how long you slept: an alarm in deep sleep leaves ten to thirty minutes of fog, an alarm in light sleep does not. Cycles average 90 minutes but range from 70 to 120, so aim for the window rather than the minute.

Walk through the night from a 8:15 am lights-out: asleep by about 8:30 am, into the first stretch of deep sleep around 8:50 am, first REM period near 9:45 am, the halfway point of the night at 12:15 pm, and the longest REM period of the night starting around 3:25 pm — which is what a 4:00 pm alarm at the end of cycle 5 lets you finish.

All bedtimes for a 4:00 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

4:00 pm: the alarm that gives a 12-hour night shift five full cycles

Twelve-hour nights, 7 pm to 7 am, leave twelve hours for everything else, and this is the alarm where the arithmetic closes. Off at 7:00 am, lights out at 8:15 am, five cycles, up at 4:00 pm, three hours before the next shift begins. Seven and a half hours of sleep, an hour and a quarter to get home and wind down, three hours to eat, travel and see anyone: that is the whole day. There is no room for a sixth cycle, since 6:45 am comes before the shift ends, and little reason to settle for the four-cycle 9:45 am unless something holds you up.

Because the margin is that thin, protect the front of it. Shortened day sleep is one of the most common problems in the shift-work reviews, and what shortens it is usually mid-morning noise and light: by 10 or 11 am you are in the later cycles, when sleep is lighter and easier to break. A phone on do-not-disturb, a note on the door and steady sound cover most of it. Caffeine for a 8:15 am bedtime ends at 2:15 am, a little past the midpoint of a twelve-hour night. On a run of three or four of these shifts, keeping the same two times every day is what keeps a window this short predictable.

Every alarm in the 4 pm hour

Lights-out times for each alarm · last coffee = six hours before the five-cycle bedtime (Drake 2013) · full grid on the open data page

If you can't fall asleep by 8:15 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 8:15 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, 9:45 am, is only a cycle away.

Try a different time