I gradually tighten my diffs over the course of a pack or two after rebuild to slowly seat the ball in place. I try to avoid cranking them down tight too quickly to avoid dimpling the rings.
With the ease of which the diffs can be adjusted, it makes it easy to do a slow lap (making sure to get a nice amount of both left and right turns to get the diff action working), bring the car in, tighten it a little and go back out to continue running through the battery pack.
Unfortunately I know of no guideline to 'tighten diff x number of turns' to set it initially...I just use the prior mentioned method and continue until it no longer slips and they give me the handling characteristics that the track requires.