We have until 30 days after get back to Brazil, to justify our vote. We have to go to to the nearest electoral office, show copies of our passport and fly ticket.
The voting is compulsory in Brazil, so if we don't vote, we can suffer some limitations, as well not to apply for puplic tender or to provide vestibular.
It's a funny way to do democracy in Brazil but law is law, we have to follow it.