Karachi is 10 hours ahead of Ottawa
There is no standard 8-to-6 overlap. Someone joins early or late.
Ottawa and Karachi are 10 hours apart, and that gap is wide enough that their normal 9-to-5 workdays never quite touch. If you meet regularly, fix one off-hours slot and rotate it between Ottawa and Karachi so the burden doesn't fall on one team. Remember that Ottawa shifts for daylight saving and Karachi doesn't, so recalculate the overlap after each clock change.