Supposedly, the caravan used to arrive here once an hour around the half-hour mark; but that schedule no longer applies, and the interval appears to simply be however long it takes to travel to the north and back. Super-Seller 680 is only available for a short time while the caravan is stopped. If you get there late, it may even disappear while you are shopping. If you need one of the unusual recipes the it sells, you will have to wait (or return) for its return.
Of most interest are the rare cooking recipes (only one per stop) from this vendor:
Recipe: Mystery Stew can only be bought here for the Horde, whereas many Alliance vendors have this recipe.