Hanoi is 5 hours ahead of Munich
Best overlap: 8:00 AM to 1:00 PM in Munich is 1:00 PM to 6:00 PM in Hanoi.
Shoot for 8:00 AM to 1:00 PM in Munich; your Hanoi colleagues will see that as 1:00 PM to 6:00 PM. Hanoi is 5 hours ahead of Munich, so the practical overlap is about 5 hours — generous enough for meetings, tight enough to be worth booking ahead. Note that Munich follows daylight saving while Hanoi stays put, so the times above drift by an hour seasonally.