Scheduled Athens arrival time from Phila on May 30th is 9:15A, with departing time to Naxos 11:30A. From posts read here 2 hours seems reasonable, BUT if we miss the 11:30A flight, how are the chances we get put on 2:10P flight? Wondering is a Friday flight at the end of May a heavily traveled flight? Thank you in advance!
There are still 3 other flights to Naxos with Olympic after the 11:30 a.m. flight.
So even if you miss your flight I think you will have a good chance of getting 2 seats on one of the following flights.
Check the Olympic Changes & Cancellations page, fees may apply depending on the case
https://www.olympicair.com/en/travel-information/changes-and-cancellations/
And remember, on flights to Naxos (on ATR42 turboprop aircraft) the baggage size allowances is smaller than usual.
I would buy the class of ticket that allows you to change your flight without penalty. That is what I have done although have not ever used it.
But cheap insurance.