A full sleep cycle actually only takes about 2 hours and in a 24 hour period you need 4 - 5 of these. The length varies from person to person. Quality is a huge factor as well. 5 meh quality cycles could leave you worse off than 4 great cycles.
The 8 hour night is actually a fairly modern thing. Historically, people would work hard during the hours of light, get home, take a 2 hour or so nap and then be awake for a while to do things like write, read, be with the family and so forth. A lot of cultures also have the siesta and so forth. Even NASA had a study where they found it more beneficial to do 3 - 4 cycles then a 4th or 5th cycle mid/late day in which people were most alert after the final cycle and were typically more alert through the day than those sleeping 4 - 5 cycles in a row.
Some famous people in history have even been known to sleep in individual cycles, taking 3 2 hour cycles per day in which people assumed they never slept. some 3% of the population function fully at only 6 hours and if you were to spread this out in 2 hours chunks over 24 hours.. yeah, it would seem like you never sleep, but really you are getting plenty if you can genetically handle 6 hours.
(Wrote a paper on the history of sleep for one of my archaeology classes)
Ok, end of weird historical/cultural post.
