I am not sure what customs you are referencing.
AA website cannot sell a ticket that is below the MCT for that transit for the type of flights being booked (D to I in this case). However, they are telling you that the connection time is rather low. I don't know if you have an earlier flight option to CLT or wish to take a later flight to the island.
When operations are going well, no issue. When there is a problem, then you are likely to have an issue with either or both flights.
Rasheed