Barcelona is 4 hours behind Islamabad
Best overlap: 12:00 PM to 6:00 PM in Islamabad is 8:00 AM to 2:00 PM in Barcelona.
For the smoothest call, aim inside 12:00 PM to 6:00 PM in Islamabad, i.e. 8:00 AM to 2:00 PM in Barcelona. Barcelona is 4 hours behind Islamabad, but you'd hardly notice — 6 hours of shared hours makes this feel like working in neighbouring time zones. Note that Barcelona follows daylight saving while Islamabad stays put, so the times above drift by an hour seasonally.