Have done this in Nov/Dec. 2006:
Walk to immigration ............ 15 min
Immigration........................ 40 min
Baggage............................ 15 min
Customs............................ 10 min
Get ARS from ATM............... 10 min
To taxi.............................. 5 min
To city.............................. 45 min .... to AEP same or a little more.

You have plenty of time, even if the plane is late.
I took a (old/lousy) taxi from the booth outside the terminal building. Next time I would get a (better) car/taxi (?) from the companies inside the terminal.
If you can, visit also the Brazilian side of the falls, it's nice too!