If you want to increase PI time you can hold in the double shot button. Keep it pushed until you want it to stop and let go.
As far as the original question I start counting when the first drip hits the glass

Randy

This is one of those questions that just won't go away

I record the pre-infusion time and the pour time separately. That way I know what I have done, and can return to it or modify it on subsequent shots. In this case, two numbers are better than one.

That's a really good answer...not sure this has come up before. It relates to the ultimate goal...the only thing that matters most is the taste in the cup.

mathof wrote:I record the pre-infusion time and the pour time separately. That way I know what I have done, and can return to it or modify it on subsequent shots. In this case, two numbers are better than one.

This is exactly what I do. Length, flow rate, and pressure of preinfusion affect the shot, as do the same parameters of the extraction itself, in a shot limited to two phases. The matrix becomes even more complicated when you can do multi-phase extractions with a Hydra, DE1, Mina, or Vesuvius.The fun is when you have consistency of grinder, machine parameters, and barista technique, you can actually begin to grok how these parameters can be manipulated for the desired effect in the cup.