Frankfurt is 1.5 hours behind Tehran

Best overlap: 10:00 AM to 6:00 PM in Tehran is 8:30 AM to 4:30 PM in Frankfurt.

Keep meetings inside 10:00 AM to 6:00 PM in Tehran — that maps to 8:30 AM to 4:30 PM in Frankfurt. Frankfurt is 1.5 hours behind Tehran, but you still share a generous 8 hours of overlap, so scheduling is easy and there's room to move a meeting when you need to. These times hold for most of the year, but Frankfurt's daylight saving (which Tehran doesn't use) shifts them by an hour twice annually.