Tehran is 6.5 hours ahead of Brasília
Best overlap: 8:30 AM to 11:30 AM in Brasília is 3:00 PM to 6:00 PM in Tehran.
Shoot for 8:30 AM to 11:30 AM in Brasília; your Tehran colleagues will see that as 3:00 PM to 6:00 PM. A 3-hour overlap gives you a workable daily window; aim for earlier in it to avoid clipping the end of someone's day.