Your score is dependant upon how fast you see the developing hazard.
In the test you are scored out of 5 for each hazard.
The scoring window is divided into 5 equal segments. If you click during the first segment you score 5 points. If you click in the second segment of this window of time you will score 4 points, then 3, then 2 and then in the last segment 1.
At the end of the actual test your scores are added together. The maximum score is 75. To pass you need a score of 44 (58%). This means on average you need to spot a hazard within a couple of seconds of it developing in order to pass.
In the hazard perception practice you will pass if you spot the hazard within this time period.
This is to help you train to spot each hazard early and therefore get the best possible result in the exam.