It felt to me like the parry happened quite suddenly and I couldn't really grasp its duration and working very quickly. It also involved all arrow keys.
It could be that there wasn't a very apparent visual indicator on the player.
For example, imagine a offensive style game, where you play as a knight. The knight holds a sword, which, when swung, plays some telegraphed animation, which gives the player feedback about things like the attack's duration. This makes the whole process of aiming the swing of the sword and attacking with it easier to grasp.