Ask anyone who has lived/worked in different time zones and the answer to this is "no". Humans are awake during the day, so it makes sense to have a system that identifies when daylight occurs in any given place. Otherwise, if the entire world has the same time (i.e. 4am now in all places worldwide), you lose that indicator of daylight. Hence, I would have to rember unique working-day (daylight) times for all places worldwide when I'm working and that shifts the information burden in the wrong direction.