Physiologically there's no difficulty in pushing your circadian around. Heck, various studies have shown that in isolation people's clocks will drift by an hour

Physiologically there's no difficulty in pushing your circadian around. Heck, various studies have shown that in isolation people's clocks will drift by an hour or more a week. Culturally though, there is a preferred cycle, and it's some weighted average of the cycle of all the people you interact with. Moving from Chile to Peru and shifting your cycle 2hrs _to match the Peruvian clock_ isn't so bad, but if you shifted 2hrs the other way you'd find it a lot more painful. This is the problem with shifting school hours: not the hours themselves, but how they interact with everyone else's hours. Finally, there is a privileged circadian, and it's the Sun's. Free, global lighting is just too good to pass up on.