+1.
Explain you were going in for a meeting, it was already going to be tight but now is impossible, etc.
Worked for me with changes smaller than that.
Back in June, I called a couple more times, and AA reps were being difficult about it.
I wasn't in such a rush for the refund, so I decided to give it a wait.
Checked today, and there was another schedule change, involving new flight numbers, and an additional 40 minute delay, bringing the total delay to 1H 40M.
So I called in again, and rep immediately agreed to cancel the ticket, for refund to credit card - no questions asked.
Finalized in less than two minutes.
I asked for some confirmation or record for my refund to credit card request, but rep says they do not provide that.
So I just hope I get the refund to credit card as she said, and not an airline credit.