Note that it will be super busy on the weekends, as you do not need tickets, so a lot of locals will go there, as if it were a regular mall. Last time I went, it was the end of February (slow time for disney), and rained all day long (remember, outdoor mall). 3+ hour waits for any restaurant. And shopping became more difficult (but not as bad as in park during the peak holiday).
Our flight got canceled, so we ended up going back on a weekday. We basically owned the place. Hardly a soul. Traffic picked up late afternoon/early evening, but then I remembered what many park guests do. You see, Animal Kingdom tends to close early, so many people hop a bus and spend the rest of their day at the marketplace.
Now then, my advice, go here on your first day. By the time we landed, and checked in to our hotel, it was noon. Don't wanna waste a park day on something like that. I was able to shop all the disney merchandise. When it came time to go to the parks, I didn't feel compelled to waste time shopping there, as the Disney marketplace pretty much had the same things. There were a few items that were unique to the parks, but that just meant that I mostly just walked into each store, and then back out, just to confirm whether or not it was something I had already seen. Shopping for such things is a big part for me, so I didn't feel like I was missing out when we tried to cram as much activities as we tried to. This saved a lot of park time for us.