Shanghai is 7 hours ahead of Geneva
Best overlap: 8:00 AM to 11:00 AM in Geneva is 3:00 PM to 6:00 PM in Shanghai.
If you set up a recurring sync, 8:00 AM to 11:00 AM in Geneva (3:00 PM to 6:00 PM in Shanghai) is the natural home for it. You share roughly 3 hours a day. That's enough for regular meetings, but treat the window as prime time and guard it. Remember that Geneva shifts for daylight saving and Shanghai doesn't, so recalculate the overlap after each clock change.