"Taiwan visa maximum stay clarification" confirms that for Taiwan visa exempt stay you start counting the number of days after the day of arrival (redundantly, as the information is available on governmental websites). That is NOT my question.
My question is what is the "day of arrival"? Is it when your plane was scheduled to land? Is it when your plane lands? Is it when you pass immigration? (This information does not seem to be available elsewhere.)
So, for example, if you have a late night flight and dawdle and don't pass immigration until after 12am, does that count as arriving the day our plane landed or the day we passed immigration ?