I'm getting a 15-day visa on arrival in Vietnam as a tourist. If I plan when to fly in and when to fly out (maximizing the duration of my stay) do I have to include the date of arrival and departure in my calculation?
A 15 day Vietnam VOA allows you to stay in the country for 15 days ... pretty simple really. The day you arrive is Day 1. The day you depart needs to be Day 15 or sooner. Like most countries the counted day starts at midnight and ends at midnight, so entering through immigration at 11:59pm still counts as Day 1. And departing at 11:59pm on Day 15 is still Day 15 (hope there are no lines if you try that ;-). I actually do not know of any countries that stamp date & time of entry then count days as 24 hour periods from that time, like car rental companies.