When I was in ATH a week and a half ago on Sunday, it was so crowded they shut the doors to only allow BIZ class passengers in. So no AMEX/PP until 1300 when most Atlantic crossings are either boarding or already departed. Every 3rd party lounge in the airport Schengen or not.

Just be warned and have a backup plan if you see the check in hall so packed you can barely move about. ATH is not a particularly comfortable airport outside of the lounges.