Stockholm is 6 hours behind Beijing
Best overlap: 2:00 PM to 6:00 PM in Beijing is 8:00 AM to 12:00 PM in Stockholm.
Both offices are open during 2:00 PM to 6:00 PM Beijing time, which is 8:00 AM to 12:00 PM in Stockholm. You've got a decent 4-hour window. Set a recurring time near 2:00 PM in Beijing (8:00 AM in Stockholm) and stick to it. Just remember Stockholm changes its clocks for daylight saving and Beijing doesn't, so confirm the overlap whenever the seasons turn.