Barcelona is 1.5 hours behind Tehran
Best overlap: 9:30 AM to 6:30 PM in Tehran is 8:00 AM to 5:00 PM in Barcelona.
Shoot for 9:30 AM to 6:30 PM in Tehran; your Barcelona colleagues will see that as 8:00 AM to 5:00 PM. Barcelona is 1.5 hours behind Tehran, but with 9 hours of common ground you can hold morning or afternoon meetings without anyone working odd hours. Daylight saving complicates things slightly: Barcelona observes it, Tehran doesn't, so the difference flexes by an hour part of the year.