Reykjavik is 3.5 hours behind Tehran
Best overlap: 12:00 PM to 6:00 PM in Tehran is 8:30 AM to 2:30 PM in Reykjavik.
Your shared working hours run 12:00 PM to 6:00 PM in Tehran (8:30 AM to 2:30 PM in Reykjavik). With 6 hours in common, treat scheduling almost as if the two cities were in the same region.