Vancouver is 14 hours behind Ho Chi Minh City
There is no standard 8-to-6 overlap. Someone joins early or late.
Given Vancouver is 14 hours behind Ho Chi Minh City, the realistic answer is that there's no convenient shared slot during normal business hours. Catch the edges of the day: the last hour for Ho Chi Minh City or the first hour for Vancouver is usually the least painful option. Just remember Vancouver changes its clocks for daylight saving and Ho Chi Minh City doesn't, so confirm the overlap whenever the seasons turn.