Tehran is 1.5 hours ahead of Barcelona
Best overlap: 8:00 AM to 5:00 PM in Barcelona is 9:30 AM to 6:30 PM in Tehran.
Plan around 8:00 AM to 5:00 PM in Barcelona, which is 9:30 AM to 6:30 PM in Tehran, to catch everyone during office hours. The overlap is wide at 9 hours, so you can protect mornings for deep work and still find plenty of meeting time. Note that Barcelona follows daylight saving while Tehran stays put, so the times above drift by an hour seasonally.