Houston is 10 hours behind Karachi

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

A 10-hour difference puts Karachi and Houston out of sync — when one team is mid-morning, the other is fast asleep. Consider rotating the inconvenience: one week Karachi takes the early call, the next week Houston does. Remember that Houston shifts for daylight saving and Karachi doesn't, so recalculate the overlap after each clock change.