Barcelona is 6 hours behind Shanghai
Best overlap: 2:00 PM to 6:00 PM in Shanghai is 8:00 AM to 12:00 PM in Barcelona.
Both offices are open during 2:00 PM to 6:00 PM Shanghai time, which is 8:00 AM to 12:00 PM in Barcelona. Roughly 4 hours of common time means scheduling is manageable; just avoid the very edges of the window. Heads up: because Barcelona changes its clocks and Shanghai doesn't, the difference moves by an hour twice a year. Confirm the overlap around the DST switch.