Philadelphia 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 Philadelphia.
For a call that suits both sides, look at 3:30 PM to 6:30 PM in Tehran / 8:00 AM to 11:00 AM in Philadelphia. You share roughly 3 hours a day. That's enough for regular meetings, but treat the window as prime time and guard it. Because Philadelphia and Tehran don't both observe daylight saving, plan to re-check the overlap around March and November.