Most likely the date it'll arrive at their store. Some probably won't put them out on display/for sale until Sunday.
I know my GS doesn't break street date, so at the very least, if those dates are correct, I don't have to worry about them selling Shulk a day or two before the 13th.
You can check (maybe call or ask in person when you can buy her), but it seems she might not be available for purchase until the 2/1 date.
& wish I could sell my copy of Xenoblade. Tried the BST thread but no luck, might have to finally give in & put it up on eBay or Craigslist or something.