BA has reflected the time change on the existing booking and automatically rebooked.
Normally this should generate an email saying how sorry they are. OP seems not to have got it.
The OP would prefer to fly three days earlier.
But since it has been moved later and by less than 1 hour, there will be no option to say it is an invalid flight connection so must be rebooked.
Personally I wouldn't chance it by changing it on the AY website. They say you are on the hook for any change fees and fare difference. You may find you have ended up making a new one way cash booking and your Avios booking cancelled with no way to reinstate it.