Firstly, for sprinters reaction time is super important. The difference of lets say 50ms, is in the end meaningfull when it's a 100 meter race. 100ms is considered a false start beyond human capabilities.
So if you try to say to me with a straight face that you can do 40ms you should call Guiness book of records since 101ms is the fastest reaction time ever measured (at least from what I googled).
Sure you can guess and get a 40ms on the screen but that doesn't mean anything.