DIM only looks for new products to download when it is first started or when you hit one of the buttons in the upper right corner of the window.  That said, it seems to take a little while between when you check out at the store and the information finds its way into whatever data base DIM uses. I've never really tried to measure how long it takes. It maybe in the 5 to 20 minutes range.  It may depend on the load on store website at the time.

That has recently changed. Finishing an order should automatically refresh your available file list. And If it doesn't, then it is set to refresh within 5 minutes of when you place your order.