Game-based assessments test how quickly and accurately you respond while other things try to distract you. Only the boxed arrow in the centre matters.
Press too early (before the arrows appear) and it counts as too early. Take longer than the time limit and it counts as too late.
You have 0.62 seconds to respond each time, and sometimes there are three arrows on each side. That is the pace to train at.
Keep your eyes fixed on the centre, not on the whole row. Rest a finger on each key so you are not moving your hand. If you make a mistake, forget it straight away: the next trial is already coming. Accuracy first, then speed.