Presumably because opening/working hours remain the same by the clock when we switch (or when you are on the edge of a zone as in some of the studies) rather th

Presumably because opening/working hours remain the same by the clock when we switch (or when you are on the edge of a zone as in some of the studies) rather than adjust, and they are currently more optimal for one of those. At any rate, I also strongly suspect it doesn't matter which one is picked but only as long as everything else is adjusted around it.