Stockholm is 3 hours behind Karachi
Best overlap: 11:00 AM to 6:00 PM in Karachi is 8:00 AM to 3:00 PM in Stockholm.
For the smoothest call, aim inside 11:00 AM to 6:00 PM in Karachi, i.e. 8:00 AM to 3:00 PM in Stockholm. Stockholm is 3 hours behind Karachi, but with 7 hours of common ground you can hold morning or afternoon meetings without anyone working odd hours. Note that Stockholm follows daylight saving while Karachi stays put, so the times above drift by an hour seasonally.