I'm going to live until I'm 82, but if I sleep 6 to 8 hours a night instead of 4 to 6, I'll live to be 83.
So I'm 26 now, 83 minus 26 is 57 years to go. 57 years worth of 2 hours extra sleep a night means 57 x 365 x 2 = 41610 extra hours without consciousness you'd have to take into consideration. Keeping in mind a year in total only has 8760 hours, it might be better not to change my sleeping pattern.