Madrid is 4 hours ahead of Brasília
Best overlap: 8:00 AM to 2:00 PM in Brasília is 12:00 PM to 6:00 PM in Madrid.
The overlap falls at 8:00 AM to 2:00 PM in Brasília, or 12:00 PM to 6:00 PM if you're in Madrid. Scheduling is forgiving here: with 6 hours of overlap, a missed slot just means picking another one the same day. Just remember Madrid changes its clocks for daylight saving and Brasília doesn't, so confirm the overlap whenever the seasons turn.