The amount you can dispense before the 1st "click" varies. Some pumps blast gas out at a high rate and will "click off" sooner than one that dispenses more slowly, since the gas will hit the tank's neck quicker.

Think of it like filling a bucket from a garden hose with a nozzle that allows you to regulate the water flow. The faster the water flows, the quicker the higher the "wave action" of the water in the bucket, and the sooner you have to slow the flow down in order to fill the bucket without water spilling over the top.