Anyone who sleeps more than six or seven hours, he is a Kumbhakarna. Kumbhakarna was the brother of Ravana. He was sleeping six months, and six months he was awake. That means anyone who sleeps half the, out of twenty-four hours, anyone, if he sleeps twelve hours, he's a Kumbhakarna. So at least I think that one should not sleep more than seven hours utmost. That is sufficient, sufficient, seven hours. So you can sleep six hours at night and one hour to rest in daytime. That is sufficient. But if you sleep more than that, then you are Kumbhakarna. You should adjust things.
(From Srila Prabhupada's lecture on Srimad-Bhagavatam 6.3.18 – Gorakhpur, February 11, 1971)