Going to tag onto this as our situation is similar. We would be arriving at EZE from GRU (Air Canada) at 15:10 on a Sunday and could book 18:45 flight out of AEP to go to IGR (Aerolineas Argentinas), so, by necessity not on the same ticket. We would only have hand luggage. Otherwise, we are spending the night. What are our chances of having this work and, realistically, how late could our AC flight be and still make the transfer? Does AR have online check in?