Bucharest is 1 hour behind Istanbul
Best overlap: 9:00 AM to 6:00 PM in Istanbul is 8:00 AM to 5:00 PM in Bucharest.
Aim for 9:00 AM to 6:00 PM Istanbul time — that's 8:00 AM to 5:00 PM over in Bucharest. With 9 hours of daily overlap, these two cities are an easy pairing; almost any reasonable hour works. Remember that Bucharest shifts for daylight saving and Istanbul doesn't, so recalculate the overlap after each clock change.