Mexico City is 3 hours behind São Paulo
Best overlap: 11:00 AM to 6:00 PM in São Paulo is 8:00 AM to 3:00 PM in Mexico City.
The overlap falls at 11:00 AM to 6:00 PM in São Paulo, or 8:00 AM to 3:00 PM if you're in Mexico City. The 3-hour gap barely gets in the way — you've got 7 hours of overlap, so pick whatever time fits the agenda.