The Brazilian parks requires no more than 4 hours of time and that would include the additional bird sanctuary outside of the park entrance.
The Argentine park requires an entire day in order to have a good look.
You should plan on staying on the Argentine side since you would be spending more time there.
RicardoBA is right that 4 hours is enough on the Brazilian side. I would suggest two days on the Argentinian. When we were there there was a big discount on the entrance fee for the second day. There is so much to see on the Argentinian side.
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