Portland is 16 hours behind Shenzhen
Best overlap: 8:00 AM to 10:00 AM in Shenzhen is 4:00 PM to 6:00 PM in Portland.
Schedule calls for 8:00 AM to 10:00 AM in Shenzhen — your colleagues in Portland will be online from 4:00 PM to 6:00 PM. With overlap this short — around 2 hours — a recurring slot at 8:00 AM in Shenzhen (4:00 PM in Portland) is worth its weight in gold. Be careful with invites: Portland is on the previous day, so a Monday meeting for Shenzhen may land on a different day there. Remember that Portland shifts for daylight saving and Shenzhen doesn't, so recalculate the overlap after each clock change.