Hanoi is 13 hours ahead of Denver

There is no standard 8-to-6 overlap. Someone joins early or late.

Denver and Hanoi live on different parts of the day. With 13 hours between them, standard working hours simply don't meet. Make the most of handoffs — end-of-day in one city becomes start-of-day in the other, so pass work along rather than meeting live. Note that Denver follows daylight saving while Hanoi stays put, so the times above drift by an hour seasonally.