Polyphasic sleep is the process of taking short sleep periods throughout the day, rather than getting it all in one long period. One popular form entails sleeping 20-30 minutes six times per day, equally spaced every 4 hours -- meaning only 2 or 3 hours a day total.
It supposedly takes about a week to adjust to such a cycle, because your body has to readjust its own "clock" so it can learn how to REM sleep immediately, rather than much later in the cycle.
And it requires some discipline to successfully transition to polyphasic sleep -- not to mention a flexible schedule that allows for naps. It's very important to sleep at the required times and not miss sleep intervals. Missing a nap can cause a rapid crash that some time to recover from.
Read the link below for an account of someone who tried out this kind of sleep schedule, with great success.