Tehran is 1.5 hours ahead of Zurich
Best overlap: 8:00 AM to 5:00 PM in Zurich is 9:30 AM to 6:30 PM in Tehran.
Target 8:00 AM to 5:00 PM in Zurich, which lands at 9:30 AM to 6:30 PM for the Tehran side. That's a roomy 9 hours of common time each day, so finding a slot that suits everyone is rarely a problem. Daylight saving complicates things slightly: Zurich observes it, Tehran doesn't, so the difference flexes by an hour part of the year.