Hanoi is 15 hours ahead of Portland
Best overlap: 5:00 PM to 6:00 PM in Portland is 8:00 AM to 9:00 AM in Hanoi.
Keep meetings inside 5:00 PM to 6:00 PM in Portland — that maps to 8:00 AM to 9:00 AM in Hanoi. With about 1 hour of common time, this pairing rewards planning — 5:00 PM in Portland / 8:00 AM in Hanoi is the slot to defend. This window straddles two dates — Portland's today is Hanoi's the next day. These times hold for most of the year, but Portland's daylight saving (which Hanoi doesn't use) shifts them by an hour twice annually.