Karachi is 3 hours ahead of Stockholm
Best overlap: 8:00 AM to 3:00 PM in Stockholm is 11:00 AM to 6:00 PM in Karachi.
For the smoothest call, aim inside 8:00 AM to 3:00 PM in Stockholm, i.e. 11:00 AM to 6:00 PM in Karachi. That's a roomy 7 hours of common time each day, so finding a slot that suits everyone is rarely a problem. For part of the year the maths changes: Stockholm observes daylight saving, Karachi does not, shifting the overlap by an hour.