You looking at how your infotainment behaves and applying it to all “electronic crap” is the issue and I guess that’s how all of these worries start.
People probably looking at how long their laptop or some other electronic device starts up and thinking the ECU in their car is the same. Lumping it all into one basket.
A quick Google search shows modern ECU processors can operate up into the megahertz range. Mega = million, so that’s millions of cycles per second. I don’t know how much ECUs can process in each cycle, but it gives you an idea that a lot can be processed.
Another Google search shows that the CANBUS is capable of very high bitrates.
There also is no spinning hard drive to spin up.
I would also assume that everything needed to get the car started is in non-volatile memory (basically lookup tables for fueling, timing, etc), so that leads me to believe that the actual starting of the vehicle might not take much actual processing.
I‘m far from a computer wiz, but all of that tells me that startup times are not likely the limiting factor here.
Note, I’ve data-logged maybe 10-15 parameters at once before and I believe the sample rate for that is 10 samples per second. I believe that is done using spare processor processing time each cycle, so pretty fast.
I turn the key to ON for a second before starting, because the fuel pump priming noise is obvious and I’ve been conditioned to wait for that cycle to end. It’s only a second, so the dash hasn’t even come to life and my radar detector hasn’t gone through it self-check yet. I have gotten in and started it right away and there is not difference that I can tell.
My wife’s vehicle has pb start, so no idea what it does with the fuel pump.