I live at 59.3 and dark curtains are not too common, most house I saw have some kind of shades or fluffy curtains, both don't block light > they concluded the

I live at 59.3 and dark curtains are not too common, most house I saw have some kind of shades or fluffy curtains, both don't block light > they concluded the human clock was 25.1 hours You keep quoting questionable or out dated research, the 25 hours figure seems to be wrong [0] > Early research into circadian rhythms suggested that most people preferred a day closer to 25 hours when isolated from external stimuli like daylight and timekeeping. However, this research was faulty because it failed to shield the participants from artificial light [0] https://en.wikipedia.org/wiki/Circadian_rhythm#Humans https://en.wikipedia.org/wiki/Circadian_rhythm#Humans