While driving with ACSES on when I get a big drop in maximum authorised speed I have no time to penalty countdown so unless I apply full service I get a penalty brake application.
Acses, according to train engineers qualified on the route, only counts down when approaching a red aspect. You'll see it when pulling into Providence
From what Matt was saying on stream last week you acknowledge the downward speed change, apply restriction brakes and then you should be fine. That the HUD throws a wobbly may or may not be relevant
Brake in "succession". On the ACS-64, it's right after 64% (I wonder if that's on purpose by the design engineers)