The salt is added in the brine to cure it and for texture. Then have to soak it in fresh water to remove the salt that was in the brine so it will be eatible.
To answer the question about how long to let the rub stay on it, I let my first one last week go with the rub on it for 7 days. You can also take it a little longer.
My arsenal, Stumps Clone, Two Modified offsets, open pit with grate and rotisserie,UDS, and a free to me Weber One Touch Silver 18.5" kettle