A University of California, San Diego psychiatry study of more than one million adults found that people who live the longest self-report sleeping for six to seven hours each night. Other studies show that sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality. source
I always thought getting less that 8 hours sleep was bad for you, but it seems it's actually good for you.
Heres another thought, say you sleep 8 hours and you change to 6 you gain 2 hours a day.
2 hours x 360 days a year = 720 hours gained
720 hours divided by 24 hours to get days = 30 days gained per year
You have just created your 13 month year
after 12 years of 6 hour sleeping you have gained a year. in reality this is more because while a day is 24 hours we are usually only awake for 16 of those hours.
720 divided by 16 = 45 days per year