UPDATE - In preparation for my flight I just went to AEP to ask them in person if you can pay the fine there. And voila - you can pay the overstay fine at AEP.
So to summarize.
You can pay the overstay fine at both AEP and EZE prior to your flight. You do not need to go to migraciones before - you can simply pay the fine at the airport as you had been able to do previously. I'd recommend giving yourself at least an extra hour to pay it. I believe that the migraciones counter at both airports is open 24/7 but I cannot confirm that with 100% certainty.
So to summarize.
You can pay the overstay fine at both AEP and EZE prior to your flight. You do not need to go to migraciones before - you can simply pay the fine at the airport as you had been able to do previously. I'd recommend giving yourself at least an extra hour to pay it. I believe that the migraciones counter at both airports is open 24/7 but I cannot confirm that with 100% certainty.
