Istanbul is 2 hours behind Islamabad
Best overlap: 10:00 AM to 6:00 PM in Islamabad is 8:00 AM to 4:00 PM in Istanbul.
The overlap falls at 10:00 AM to 6:00 PM in Islamabad, or 8:00 AM to 4:00 PM if you're in Istanbul. The 2-hour gap barely gets in the way — you've got 8 hours of overlap, so pick whatever time fits the agenda.