Comment by freefaler

24-18 = 6 hours "non-working" time. Eating, washing and shitting is min 1 hour/day.So 5 hours of bed time with around 4.75 hrs of sleep at most, because we don't fall asleep right away.

The math doesn't work long term. It may be kept for 1-2 months even when a person is 21 yrs old, but I doubt it it can be sustained more than that.