Think you find stop means stop, all four wheels must stop rotating. There is no definition or defined time to stop as far as I am aware.
A court would determine a stop by the definition from a dictionary.
you must show that there was no forward movement and it lasted so that it was a stop not a roll...
the three seconds would probably come from the look left look right look left, the time it takes to undertake those obs.
I stand to be corrected ..
In my experience if your wheels stop rotating you would not get a ticket, and if you did you could argue in a court, if they accepted your account the Court would dismiss the charge of failing to stop.
You must stop before the line and not over it....
mat some of these junctions you still need to then crawl forward to ensure its clear, that's why you must stop before the line.
one sure way to cover your rear end, get a camera on your dash, great evidence should you ever need it..,