Shanghai is 12 hours ahead of Philadelphia
There is no standard 8-to-6 overlap. Someone joins early or late.
Given Shanghai is 12 hours ahead of Philadelphia, the realistic answer is that there's no convenient shared slot during normal business hours. Catch the edges of the day: the last hour for Shanghai or the first hour for Philadelphia is usually the least painful option. The window above shifts seasonally: Philadelphia keeps daylight saving while Shanghai ignores it.