Beijing is 12 hours ahead of Philadelphia

There is no standard 8-to-6 overlap. Someone joins early or late.

Beijing is 12 hours ahead of Philadelphia, which is far enough that a normal 9-to-5 in one city never reaches the other's working hours. One practical option: Philadelphia dials in early while it's still late afternoon or evening in Beijing. Remember that Philadelphia shifts for daylight saving and Beijing doesn't, so recalculate the overlap after each clock change.