I read about a very interesting research that was done where they too people and placed them in undeground bunkers (willingly). They then took away all references to time and they were given loads of creative stimulation.
They had no reference to 'sleeping time' or eating time ec.
They found that the average person only slept 4.4 hours a day. It turns out that most of people only sleep 8 hours out of habit or maybe out of not knowing what to do with their lives?