Shanghai is 6 hours ahead of Oslo
Best overlap: 8:00 AM to 12:00 PM in Oslo is 2:00 PM to 6:00 PM in Shanghai.
The overlap falls at 8:00 AM to 12:00 PM in Oslo, or 2:00 PM to 6:00 PM if you're in Shanghai. You've got a decent 4-hour window. Set a recurring time near 8:00 AM in Oslo (2:00 PM in Shanghai) and stick to it. Just remember Oslo changes its clocks for daylight saving and Shanghai doesn't, so confirm the overlap whenever the seasons turn.