Where does the day officially begin and end?

Answer 1

Wherever you are, there is an official beginning and end to any given day. It is called midnight. The first place that a given day occurs is just to the west of the International Date Line. The date line goes through the middle of its time zone. At midnight at that time zone, a new day first appears in the half time zone to the west, and the last place to start the day that is already progressing every place else is the half time zone to the east. So that half time zone to the east is also the sliver of earth where the last of a given day comes to an end. The 'defined' time zones, and the date line, are really theoretical and they are not governed by any one nation or by international law. Most of the time zone boundaries closely follow the 'defined' limits, but many nations make exceptions for the sake of their own internal and commercial needs.