With the egates the long immigration lines of old are no longer there, so assuming you have an egate eligible passport that part is pretty easy and quick, the biggest unknown that can slow you down is luggage retrieval it can be very slow at terminal five, then you need to go get on the train to change terminals you could be lucky and hit the train right as It is leaving or you could have to, wait ten or so minutes, then there is security at T2 if you are flying business class and can use the fast track lane it shouldn’t be horrible, I have never checked in luggage on Aegean so I can’t speak to that. In the end you should be ok on time but it isn’t going to be easy especially with luggage, can you get on the aa flight from jfk rather than the ba flight, aa comes into terminal three luggage tends to be quicker and you can walk to t2, points on the aa will be more but copay less.