THE NANO-NAP: 10 to 20 seconds. Sleep studies haven’t yet concluded whether there are benefits to these brief intervals, like when you nod off on someone’s shoulder on the train.
THE MICRO-NAP: two to five minutes. Shown to be surprisingly effective at shedding sleepiness.
THE MINI-NAP: five to 20 minutes. Increases alertness, stamina, motor learning, and motor performance.
THE ORIGINAL POWER NAP: 20 minutes. Includes the benefits of the micro and the mini, but additionally improves muscle memory and clears the brain of useless built-up information, which helps with long-term memory (remembering facts, events, and names).
THE LAZY MAN’S NAP: 50 to 90 minutes. Includes slow-wave plus REM sleep; good for improving perceptual processing; also when the system is flooded with human growth hormone, great for repairing bones and muscles.
Check out this interesting infographic to learn more about napping health benefits, the culture of napping

and the famous nappers:

Source:

http://positivemed.com/2012/09/17/napping/