Athens is 0.5 hours behind Tehran

Best overlap: 8:30 AM to 6:30 PM in Tehran is 8:00 AM to 6:00 PM in Athens.

For the smoothest call, aim inside 8:30 AM to 6:30 PM in Tehran, i.e. 8:00 AM to 6:00 PM in Athens. That's a roomy 10 hours of common time each day, so finding a slot that suits everyone is rarely a problem. Daylight saving complicates things slightly: Athens observes it, Tehran doesn't, so the difference flexes by an hour part of the year.