Well, "cracking" is just a figure of speech for opening the throttle.
The crucial thing is that you need a flow of air before introducing and igniting fuel, otherwise you'll just burn the engine. So you crank the starter with the throttle closed until it reaches 12-15% N1. This establishes the necessary flow of air and you can then introduce fuel by opening ("cracking") the throttle.
The idle stop represents the minimum amount of fuel flow necessary for self-sustaining operation once the rpm gets up to 58%. You don't want to introduce any more than this until it gets up to speed, or again you'll cook the engine.
Until it reaches 58% you gotta keep cranking the starter to keep that flow of vital cooling air going, so stick your thumb on that button, and . . . whatever happens, don't let go !!!