Portland is 15 hours behind Ho Chi Minh City
Best overlap: 8:00 AM to 9:00 AM in Ho Chi Minh City is 5:00 PM to 6:00 PM in Portland.
Plan around 8:00 AM to 9:00 AM in Ho Chi Minh City, which is 5:00 PM to 6:00 PM in Portland, to catch everyone during office hours. Overlap is at a premium — roughly 1 hour — so claim 8:00 AM in Ho Chi Minh City (5:00 PM in Portland) for recurring calls and keep them on time. The date rolls over between them: Portland is on the previous day relative to Ho Chi Minh City during these hours. Note that Portland follows daylight saving while Ho Chi Minh City stays put, so the times above drift by an hour seasonally.