Most that participate do have guaranteed Christmas arrival, although some do require for you to upgrade to a faster shipping option for a small fee ($2.99-3.99) or even more. Just depends on the merchant. Here's the official site.
This is what they say on thier site
We have reached a point where consumers are expecting free shipping when they shop online, but in many cases it is offered when you purchase a certain amount, such as $50 or $100,” Knowles said. “To make Free Shipping Day even more unique, we are encouraging retailers to offer free shipping on all orders.”
i'm hoping Victoria Secret has free shipping on all orders so i can use the last of my secret rewards cards. if not i'm gonna have to go to the mall to spend them and i HATE the mall, especially at this time of year.