I think we need about 5-6 hours sleep. Because our body need rest and it need to recover.According to the doctors they said human need to get 6 hours of sleep in daily life.
A healthy strong person needs 6 hours of sleep daily I usually sleep for 7 to 8 hours. As you have rightly suggested 6 hours of daily sleep is beneficial for doctors. But at night I sleep at about 12 o'clock But I wake up very late in the morning