Hamburg is 7 hours behind Shenzhen
Best overlap: 3:00 PM to 6:00 PM in Shenzhen is 8:00 AM to 11:00 AM in Hamburg.
If you set up a recurring sync, 3:00 PM to 6:00 PM in Shenzhen (8:00 AM to 11:00 AM in Hamburg) 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 Hamburg shifts for daylight saving and Shenzhen doesn't, so recalculate the overlap after each clock change.