Istanbul is 5 hours behind Shanghai
Best overlap: 1:00 PM to 6:00 PM in Shanghai is 8:00 AM to 1:00 PM in Istanbul.
Keep meetings inside 1:00 PM to 6:00 PM in Shanghai — that maps to 8:00 AM to 1:00 PM in Istanbul. You share roughly 5 hours a day. That's enough for regular meetings, but treat the window as prime time and guard it.