Medellín is 2 hours behind Brasília
Best overlap: 10:00 AM to 6:00 PM in Brasília is 8:00 AM to 4:00 PM in Medellín.
For the smoothest call, aim inside 10:00 AM to 6:00 PM in Brasília, i.e. 8:00 AM to 4:00 PM in Medellín. Medellín is 2 hours behind Brasília, but you'd hardly notice — 8 hours of shared hours makes this feel like working in neighbouring time zones.