Is there a player action window during or after an individual racing test? For example, T Boromir exhausts to make a racing test after completing stage 1b. He succeeds and the excess progress is placed on stage 2b. Enough progress is placed that stage 2b is also completed and a second racing test is triggered. Is there any window during all this that T Boromir could have readied himself?

My hunch is that the answer is no, but as racing tests aren't a typical part of the game I'm unsure.