Istanbul is 1 hour ahead of Vienna

Best overlap: 8:00 AM to 5:00 PM in Vienna is 9:00 AM to 6:00 PM in Istanbul.

For the smoothest call, aim inside 8:00 AM to 5:00 PM in Vienna, i.e. 9:00 AM to 6:00 PM in Istanbul. The overlap is wide at 9 hours, so you can protect mornings for deep work and still find plenty of meeting time. Don't be caught out by clock changes — Vienna observes daylight saving and Istanbul doesn't, so the offset varies by an hour through the year.