What do you expect to happen after 3 key presses, move 3 pages? One page?
Introducing a pause isn't difficult, but I'm not seeing how that will help. As you have it, such a pause will only slow down what's already happening. Based on your thread title, it's counter intuitive to think you can stop key press code from running just because there's multiple calls to it.
There may be a way to redirect execution when there are multiple presses of the same key by using the Shift parameter, but I don't see the point in scrolling only 1 page when there were 3 presses.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.