I really can't help. I had to get a visa when I went to Argentina around 8 years ago via Brazil, which was good for 5 years, and we spent 2 nights in SAO PAULO on the way back, but we had intended to do this before we went. Don't know nuthin as far as layovers. Worse case scenario, my guess is, unless it has changed since, would be that IF you had to fork out some bucks for a visa, you best take advantage and see some of the country to make it worth your while. Visas cost me 200 bucks for two of us, (me and wife) but that was then, don't know about the now. Good luck.