Is it too late to change this? I would never, ever trust AA with a 40 minute layover, and especially in Philadelphia. Do you have other options? You will likely have to change terminals, and the shuttle service at that airport is questionable at best. Not to mention that a flight to SXM from Philadelphia will start boarding roughly 30 minutes prior to departure time. By the time your first flight lands, everybody ahead of you on the plane retrieves their belongings from the overhead bins, you get off the plane and check the board for your next departure gate ... you see my point. Would you trust a 40 minute layover at ORD of you had to go from Terminal A to Terminal F? Not to mention that your luggage likely won't make it until the following day. Do yourself a big favor and try to get this switched. I recommend a 1-1/2 hour or longer layover, especially at PHL. Good luck.