However, in part for reasons of organizationalconvenience, modern societies are structured as if all humans had the same sleep requirements; and in many parts of the world there is a satisfying sense of moral rectitude in rising early. The amount of sleep required for buffer dumping would then depend on how much we have both thought and experienced since the last sleep period.
Carl Sagan, Dragons of Eden: Speculations on the Evolution of Human Intelligence
dreams, human-behavior, sleep