https://www.aa.com/i18n/travel-info/...nd-arrival.jsp
Never had an issue with 45 minutes prior. I know if you check in electronically and do not get your bag to the check-in counter, they can make an exception if they call the ramp (sometimes). Otherwise, if it will fit through the TSA x-ray machine, they do not enforce the various airline luggage parameters; you can then gate check it to your destination. 45 minutes prior to departure pushing it at any airport, as they board 35 minutes prior to departure and AA is getting more strict about closing the flight at least 10 minutes prior to scheduled departure time.