I asked this question when we boarded our AA flight in Minneapolis, and was told that because the EHAS approval letter was for a specific flight, if it was delayed and we were outside the 120 hours we would have to fly back AT OUR OWN EXPENSE and would not be able to board. That shocked me, as delays are not typically due to any fault of the passenger!

Delta's policy may differ, this is just what we were told by AA. Also - we too had a 45 minute connection in CLT, the flights and airport were not at all busy so it was not an issue.