BA sets the MCT. It simply represents the willingness of an air carrier to accept the risks of a misconnect, including EC 261/2004 compensation. BA can, of course, waive the MCT as it sets the MCT, for any ticket, but it will not and it is not worth asking.
Several options:
1. Do nothing at the moment. Changes occur all the time. Your flight could quite easily move back to its old slot. Sooner or later you will need to do something, but if you are happy with what you booked, no need to deal with it now.
2. Ask BA to change your GLA segment to the next flight (or the next AM), but do understand that BA won't cover your hotel.
3. Ask BA to change the entire route to the next day or any other reroute which works (AA-BA combinations via other US gateways).
4. Accept what is proposed.
But, remember that you only get one free change. Thus, if you have BA change your tickets now and later decide you want something else, that later change will be subject to whatever penalties and fare differences apply to your ticket.