Copenhagen is 5 hours behind Hanoi
Best overlap: 1:00 PM to 6:00 PM in Hanoi is 8:00 AM to 1:00 PM in Copenhagen.
Shoot for 1:00 PM to 6:00 PM in Hanoi; your Copenhagen colleagues will see that as 8:00 AM to 1:00 PM. Copenhagen is 5 hours behind Hanoi, so the practical overlap is about 5 hours — generous enough for meetings, tight enough to be worth booking ahead. Seasonal note: Copenhagen uses daylight saving and Hanoi doesn't, so double-check the times in your own months — they can move by an hour.