I came to the conclusion that the human sleep cycle is not based on cultural standards.
The human sleep cycle is a biological human characteristic based on the earth's 24 hour rotation period.
1.
If we slowed the earth down to a 36 hour rotation period, we could asume that the length of daylight and night would increase in proportion.
There is about an average of 14 hours of daylight, and 10 hours of night in a 24 hour period.
Therefore. there would be about an average of 21 hours of daylight, and 15 hours of night in a 36 hour period.
Regardless of the new 36 hour day, humans would still abide by a sleep cycle that they biologically (not culturally) evolved with.
2.
If you take a person, and lock him in a dark room with no windows, that person might not sleep at the exact time that it is night outside. However, I would hypothesize that the person would abide by the biological human sleep cycle. Meaning that the amount of sleep cycles this person would go through would be roughly the same as a person outdoors.
3.
If earth had always had a 36 hour rotation period, humans would have evolved according to a cycle of 15 hours night, and 21 hours daylight. Because I have concluded that the human sleep cycle is biologically based on the 24 hour rotation of the earth. I have also concluded that if the human evolved on a 36-hour earth, the human would have evolved to have a different sleep cycle. Our bodies would probably have evolved to match the day and night cycles of a 36-hour earth.