Ottawa is 12 hours behind Hanoi
There is no standard 8-to-6 overlap. Someone joins early or late.
Hanoi and Ottawa live on different parts of the day. With 12 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. Daylight saving complicates things slightly: Ottawa observes it, Hanoi doesn't, so the difference flexes by an hour part of the year.