This leak by the retailer confirms the outed poster from a Polish site we reported earlier. However, for now, we still can't verify if this release window is for the game's worldwide release, or just for the U.K.
I used to work in GAME and Gamestation stores, and I know that these sleeves will probably be put on display by the end of the week, next week by the very latest. But there are rules for things like sharing images of promotional materials before the date on which the publisher has authorized them for display, and – obviously mindful of that – the person behind the Twitter account has promptly removed the tweet.
Given that Game Informer's upcoming Grand Theft Auto 5 blowout is almost upon us, I expect Rockstar to give an official response to all these leaks sooner rather than later.