Houston 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 Houston.
The overlap falls at 4:30 PM to 6:30 PM in Tehran, or 8:00 AM to 10:00 AM if you're in Houston. Just 2 hours of shared hours means there's little margin — set 4:30 PM in Tehran (8:00 AM in Houston) and start promptly. Because only Houston changes its clocks, the overlap above isn't fixed; expect a one-hour shift when Houston enters or leaves daylight saving.