Hanoi is 5 hours ahead of Budapest
Best overlap: 8:00 AM to 1:00 PM in Budapest is 1:00 PM to 6:00 PM in Hanoi.
Keep meetings inside 8:00 AM to 1:00 PM in Budapest — that maps to 1:00 PM to 6:00 PM in Hanoi. Hanoi is 5 hours ahead of Budapest, which gives you a solid 5-hour window. Book earlier in it and neither side is rushing. Keep an eye on the calendar — Budapest observes daylight saving and Hanoi doesn't, which nudges this window by an hour twice a year.