Naps should be shorter than 90 minutes to avoid disrupting nighttime sleep and should not be taken if they disrupt nighttime sleep.

“Never nap longer than 90min in any case.”

“I suggest a daytime nap less than 90min”

“Just make it 90 minutes or less. Again, these 90-minute cycles are really a vital constraint that we should all obey. If it's 91 minutes, don't worry. You won't dissolve into a puddle of tears. But if you're starting to sleep for an hour or more in the afternoon, that can be problematic.”

“don't nap for more than 90 minutes. And don't nap after 4:00 PM.”

“It is fine to nap in the afternoon, but don't nap so late in the day or for so long that it disrupts your ability to fall and stay asleep at night for your major sleep about, okay?”

“keep those naps shorter than 90 minutes for reasons related to ultradian cycles and so forth”

“keep them shorter than 90 minutes so you don't disrupt your nighttime sleep don't do them at all if it disrupts your nighttime sleep”