Tel Aviv is 4 hours behind Hanoi
Best overlap: 12:00 PM to 6:00 PM in Hanoi is 8:00 AM to 2:00 PM in Tel Aviv.
For the smoothest call, aim inside 12:00 PM to 6:00 PM in Hanoi, i.e. 8:00 AM to 2:00 PM in Tel Aviv. That's a roomy 6 hours of common time each day, so finding a slot that suits everyone is rarely a problem. Don't be caught out by clock changes — Tel Aviv observes daylight saving and Hanoi doesn't, so the offset varies by an hour through the year.