you'll be fine getting 6 hours a night and a little more on the weekends...
hell, this is my weekend this past weekend:
Friday night, get 9 hours, get up at 8am. Get to work at 4pm, work until 5:30 AM, go home, get to bed at 6:30
Sleep until noon (5.5 hours), back to work at 4pm. Work until 3am Get home, go to sleep by 4:30am, get up at 8:30am (4 hours), go to court. Get home from court, hoping for a nap...no such luck.
Go to work 4pm, work until 3am again. By this time I'm BEAT. I've also not had caffeine since 5pm. I had no problems falling asleep that night!!