Hanoi is 7 hours ahead of Reykjavik
Best overlap: 8:00 AM to 11:00 AM in Reykjavik is 3:00 PM to 6:00 PM in Hanoi.
Target 8:00 AM to 11:00 AM in Reykjavik, which lands at 3:00 PM to 6:00 PM for the Hanoi side. Since Hanoi is 7 hours ahead of Reykjavik, the workdays overlap by around 3 hours; 8:00 AM in Reykjavik (3:00 PM in Hanoi) makes a reliable recurring slot.