4 hours a day is good,set your alarm and obey it when it rings,it will be very hard at first,but you ll get used to it,it you feel sleepy during the day,10 minutes nap ll do just fine
About 7 hours is the ideal. If you consistently sleep less than 5 hours you triple your risk of heart disease. If you sleep 8+ hours consistently, it's a 1.5x the risk. Here is an article that recommends 7.5: http://phys.org/news145558000.html Also this sleep calculator is really helpful: http://www.web-blinds.com/resources/sleep-calculator/ You tell it when you want to wake up, it gives you a range of times to go to bed so you can wake up after completing a REM cycle and not in the middle of one which would make you grumpy.