How much sleep each individual needs can vary. There is no magic number, according to SleepFoundation.org. "While you may be at your absolute best sleeping seven hours a night, someone else may clearly need nine hours to have a happy, productive life." And a February 2015 article at LiveScience.com says that ". . . although the NSF [National Sleep Foundation] recommends that adults ages 26 to 64 sleep 7 to 9 hours, it may be appropriate for some people to sleep for as little as 6 hours, or as long as 10 hours, the guidelines say." (See Infographic below.)
If you don't get enough sleep at night, naps can help bridge the gap. (See my previous post, How To Procrastinate.) Either way, being well-rested can help you do your best work.