Aatrox's Q begins counting down before the animation ends.
Something I found incredibly frustrating when playing Aatrox was trying to Q and then reposition for the next one, only to have my Q be unavailable and on cooldown. I went into practice tool and noticed that the duration you have before Q runs out begins counting down when the ability is cast, not when the animation finishes. I think changing this so the countdown begins after the animation finishes would make Aatrox feel a lot better as it would give you more time to reposition yourself between Q casts.