The fact it's a time change only is irrelevant; any change of flight date/time is treated the same for avios purposes. (AA may offer you a free same day change when they have control of the ticket, but that's a separate issue.)

Re your query, the rules are:

- You can cancel a booking for free (full refund of avios and taxes) within 24 hours of making the booking. The agent should also let you change for free within that period. Must be done over the phone.

- After that period, you can cancel online up until 24 hours prior to departure and get your avios refunded. The only cost incurred will be the negligible taxes, so it's virtually free cancellation and you can simply rebook.

- Otherwise any change (rather than cancel and rebook) will incur a change fee. This is £35 in UK, don't know about 80USD but maybe that's with phone fee.

- Any change within 24 hours of departure you lose everything (unless AA choose to rebook you per above).