where I can find how long does parking brake quarantee wheels locked after shut-down
No guarantees on this one. If you have a good accumulator, they will hold long enough for you to walk your passengers into the terminal and have a coffee. Then run back out to stop it rolling backwards - without brake pressure.
A friend had this happen to him, and he got to the aircraft just as it started rolling. He put his foot in front to the wheel to stop it rolling. It took 4 weeks for his broken ankle to heal.