Thanks for playing!
I think it's hard to signal exactly when in the attack you should start your attack, since you can potentially parry using any melee attack, and each of them could have different frame timings. So there's no way to say "in this attack, if you start at 10f, you'll parry it at 30f" because you might just be using an attack that has 30f windup, 10f windup, or any other timing. Part of the game's design is getting a feel for each attack's timing to be able to make your own choices for which attack to use at any given point of time.
(Although in practice, the 1st normal attack ends up being the easiest to parry with for everything at the cost of not being able to win most parry interactions. )