If I understand the OP correctly he/she has already purchased both flights, and will throw away one in any case.

Buying fast track at the airport would take more time than what it saves. You could buy for the first Aegean flight if your AA flight seems to be on time. Buy for the second if it seems to be heavily delayed. I’d make the decision just before take off in PHL.

You can’t also check flightstats for similar flights around the same time (eg to FCO or IST), to see if the winds (and therefore flight times) are favorably that day. That’s a bit of a tricky play, and in no way a guarantee, but it could give some indications.