So, once you’ve decided to take a midday snooze, how long should you actually nap for? Given a person’s natural sleep cycle (where we phase through light sleep, deep sleep, and a bit of REM) lasts roughly between 90-110 minutes, Darley says the ideal nap time is 30 minutes or less—or a full hour-and-a-half sleep cycle.
If you stick within one of those timeframes, you should be able to wake up while in a lighter sleep phase. “You want to avoid waking up out of deep sleep,” Darley explains, as that will make cause grogginess. Plus, she says, “performance is impaired for about 20 minutes after you wake up during deep sleep.”
“If a person is sleeping in the middle of the day, they likely won’t take long to fall asleep,” she adds. With that in mind, consider setting your alarm for 35 or 95 minutes after you lay down, to give yourself a few minutes to fall asleep.