If the flights don't work for you, consider taking the ferry. Buquebus runs a fast ferry that takes about 2 hours, and a ferry/bus combo through Colonia that takes about 4 hours. Prices anywhere from US$40-100, plus a taxi or shuttle from EZE to downtown to catch the ferry. Overall it probably takes longer, but maybe not depending on flight schedules and layover. But it gets you there, maybe for less money, and ferries run throughout the day. Plus its a cool way to go.

I would not attempt a tight connection at EZE, as most times you will not make it...