Not sure about much regarding this free shipping deal (Maybe it was mentioned in the last Telltale Interloper, but I don't have it anymore, so I can't check).
I saw it mentioned in other threads over a week ago and tried it to see if it worked (which it did).
Not sure either when it expires, but people in several threads mention a July 31 expiration date (yes, that's today).
Because it's the weekend, I wouldn't be surprised if the promotion was still working tomorrow, though.
You'll just have to try (since Telltale works on Pacific Daylight Time, there are still almost four hours to go before tomorrow).