Another interesting data point on reacting to a "stop" signal.
Stage 17 from production nationals in 2022 was a 8 second PAR time stage. A significant number of the production shooters in the match could not finish within the PAR time, so they left targets and shots unfired. Anything over .3 seconds past the PAR time resulted in a procedural penalty. If you scroll down the results (filter by production so we're only looking at pistol shooters) and compare the "NPM" (Non Penalty Mike) column with the "Proc" (Procedural Penalty) column, you'll see how many shooters did not finish the stage, therefore were scored non penalty misses and how many of those incurred a procedural penalty for firing more than .3 seconds after the timer beep.
https://practiscore.com/results/new/184732?q_result=17
90 out of 107 pistol shooters couldn't finish the stage and had to stop at the par time. 4 of those 90 didn't react fast enough to the beep and fired at least 1 extra shot past the .3 seconds. We can break it down even further by classification: not a single GM or M shooter, the shooters with the fastest average split times, fired a shot over the time limit. I would argue that setting an arbitrary, "don't shoot faster than .25 splits because you won't be able to stop shooting," shouldn't be equally applied across all skill levels, and that shooters who can shoot much faster than that, can also stop the shooting much faster.
Again though, we are debating a point that has no legal basis in a real world shooting. If you had the legal justification to engage someone with deadly force, an extra round on the back end that comes out at .25 seconds after they are dropping a weapon or falling to the ground isn't going to turn a legally justified shoot into an unjustified one.