How long does it usually takes for a kidney stone to pass?

Most in 2 days. Most stones if they are going to pass will pass in the first 48 hours. The chances after that start to decrease. The chances probably never go to zero but after a week, the chances are probably around 50% of it ever passing.
Completely variable. The time taken for a kidney stone to pass is entirely variable and depends upon the person's hydration level, stone size, and location of the stone.