Helsinki is 5 hours behind Beijing
Best overlap: 1:00 PM to 6:00 PM in Beijing is 8:00 AM to 1:00 PM in Helsinki.
Keep meetings inside 1:00 PM to 6:00 PM in Beijing — that maps to 8:00 AM to 1:00 PM in Helsinki. With 5 hours of overlap, 1:00 PM in Beijing (8:00 AM in Helsinki) is a comfortable, repeatable slot for both sides. Remember that Helsinki shifts for daylight saving and Beijing doesn't, so recalculate the overlap after each clock change.