Dallas is 14 hours behind Shenzhen
There is no standard 8-to-6 overlap. Someone joins early or late.
Given Dallas is 14 hours behind Shenzhen, 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 Shenzhen or the first hour for Dallas is usually the least painful option. Just remember Dallas changes its clocks for daylight saving and Shenzhen doesn't, so confirm the overlap whenever the seasons turn.