Stockholm 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 Stockholm.
Keep meetings inside 1:00 PM to 6:00 PM in Hanoi — that maps to 8:00 AM to 1:00 PM in Stockholm. Around 5 hours of overlap is enough to work comfortably, as long as meetings don't drift to the end of one team's day. Because Stockholm and Hanoi don't both observe daylight saving, plan to re-check the overlap around March and November.