Atlanta is 7.5 hours behind Tehran
Best overlap: 3:30 PM to 6:30 PM in Tehran is 8:00 AM to 11:00 AM in Atlanta.
Keep meetings inside 3:30 PM to 6:30 PM in Tehran — that maps to 8:00 AM to 11:00 AM in Atlanta. You share roughly 3 hours a day. That's enough for regular meetings, but treat the window as prime time and guard it. Remember that Atlanta shifts for daylight saving and Tehran doesn't, so recalculate the overlap after each clock change.