Reykjavik is 3 hours behind Istanbul
Best overlap: 11:00 AM to 6:00 PM in Istanbul is 8:00 AM to 3:00 PM in Reykjavik.
The overlap falls at 11:00 AM to 6:00 PM in Istanbul, or 8:00 AM to 3:00 PM if you're in Reykjavik. Reykjavik is 3 hours behind Istanbul, and with 7 hours of overlap you can even run back-to-back calls without stepping outside business hours.