Shanghai is 16 hours ahead of Portland
Best overlap: 4:00 PM to 6:00 PM in Portland is 8:00 AM to 10:00 AM in Shanghai.
Target 4:00 PM to 6:00 PM in Portland, which lands at 8:00 AM to 10:00 AM for the Shanghai side. The overlap barely stretches to 2 hours, so reserve it for what really needs a live conversation and handle the rest async. Because of the gap, Shanghai is already on the next day, so confirm you're both talking about the same calendar date. Don't be caught out by clock changes — Portland observes daylight saving and Shanghai doesn't, so the offset varies by an hour through the year.