There’s stll quite a bit of controversy in the scientific community about the ideal sleep pattern for longevity. Most seem to think that if you allow your body to settle into a consistent sleep schedule, then the ideal amount would be however much you naturally sleep without an alarm.
But then a sleep researcher at U.of California, San Diego, Daniel Kripke, came out with a study in 2002 that indicated that 6–7 hours was the optimum for longevity, with a 15% decline at 8 hours.
Those findings have been widely disputed.