Dallas is 8.5 hours behind Tehran
Best overlap: 4:30 PM to 6:30 PM in Tehran is 8:00 AM to 10:00 AM in Dallas.
If you set up a recurring sync, 4:30 PM to 6:30 PM in Tehran (8:00 AM to 10:00 AM in Dallas) is the natural home for it. There's just 2 hours of overlap here, so don't leave meetings to chance — lock 4:30 PM in Tehran / 8:00 AM in Dallas into the calendar. Remember that Dallas shifts for daylight saving and Tehran doesn't, so recalculate the overlap after each clock change.