Shanghai is 5 hours ahead of Istanbul
Best overlap: 8:00 AM to 1:00 PM in Istanbul is 1:00 PM to 6:00 PM in Shanghai.
Plan around 8:00 AM to 1:00 PM in Istanbul, which is 1:00 PM to 6:00 PM in Shanghai, to catch everyone during office hours. A 5-hour overlap gives you a workable daily window; aim for earlier in it to avoid clipping the end of someone's day.