The second update send out a notification from which you can decide to download it onto your tablet. Once it is installed, the build number updates to JSS15J and you are on your merry way. The updates appear to be minor in nature, perhaps including some last second tweaks and some bug fixes.
As we told you on Friday night, Staples has sold out of both the 16GB and 32GB variants of the slab and Amazon ran dry of the 32GB model. Shipping time on the latter is now 3 to 4 weeks for new orders. Before you commit to that long a time period, we suggest checking out other retailers like Best Buy and Walmart. If all else fails, there is the Google Play Store which is accepting orders for both tablets, and will ship them no later than July 30th.