Zurich 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 Zurich.
Karachi and Zurich overlap from 11:00 AM to 6:00 PM (Karachi) to the equivalent 8:00 AM to 3:00 PM in Zurich — that's your meeting window. 7 hours of shared hours is more than enough — slot meetings wherever they're most convenient for the people involved. One seasonal catch: Zurich springs forward and falls back, but Karachi doesn't, so the gap changes by an hour for several months of the year.