Time
The fastest espresso recipe you will find anywhere would take 15 seconds from turning the button on up until the moment the shot finishes. The slowest recipe might take 45 seconds. Baristas can manipulate how long it takes to produce an espresso by grinding beans finer (into smaller particles) or coarser (into larger particles).
The Relationship Between Time and Grind
The word resistance explains how shot times and grind settings interact. If you didn’t grind the coffee at all and then you made an espresso using whole beans, all the water would come through in about 5 seconds. This is because the water could easily fit through the large gaps between beans. In this situation you would have zero resistance to the flow of water.