Istanbul is 1 hour ahead of Brussels
Best overlap: 8:00 AM to 5:00 PM in Brussels is 9:00 AM to 6:00 PM in Istanbul.
Keep meetings inside 8:00 AM to 5:00 PM in Brussels — that maps to 9:00 AM to 6:00 PM in Istanbul. Istanbul is 1 hour ahead of Brussels, but you still share a generous 9 hours of overlap, so scheduling is easy and there's room to move a meeting when you need to. Finally, Brussels observes daylight saving and Istanbul doesn't, so this window shifts by an hour for part of the year — recheck it each spring and autumn.