Well, the direction in UEFA (not in England as I understand it though?) is that advantage should not be visibly played within the penalty area and it should be considered a "silent" advantage -- because the only advantage that should accrue within the penalty area is... a goal.
From the time where the defender makes contact with the ball to the goal is about a second and a half, well within the 3-5s recommended for determining if advantage should be played.
Once the ball goes in, the Ajax players pile into the goal and the AAR and Referee rush onto the scene, so there's not really time to show the advantage signal there either, even if he was going to do so...