Grind to brew ration is 1:2.
So 17g of coffee grounds makes 34g espresso.
Get a cheapo set of digital scales that read 0.00g as 34g of espresso is not 34ml!
As said, 20 – 25 seconds. I prefer slightly longer at 30 seconds.
But this all come down to how the coffee is ground. You’d usually grind it finer or coarser to get your time correct. As yours is pre-ground, you could try adding more or less coffee to adjust the extraction time verse weight.
A fast extraction can give a sourness, lack sweetness and a quick finish. ie, once you’ve had your drink, the flavour leaves your mouth quickly.
Too long and you get bitter / dry notes.
Just play around, take notes of your recipe and mark which ones you like and don’t like. If the numbers don’t match, but it tastes great, who cares!