The main banks of international flights leave later in the evening, so EZE should be relatively quiet when you check in. As an elite customer you should be through the initial security screen and check-in in a matter of minutes.

Tax payment and the WTMD/X-ray should also be quite fast (but depending on how many security stations are open), and maybe 20 minutes at most for immigration if there are only few booths open.

Flights to the US also have gate security where they inspect your carry-on luggage and shoes, and wand you body, but that's mainly for show.

John