About the moment it starts being released.
IOW, even if they promised it tomorrow morning, if they find a major bug today, it won't be released tomorrow, so all anyone can do is make guesses, some better informed than others, but none very good. (There's too much code in a tablet to be sure that someone playing with the new UK release at Samsung doesn't find a major problem just as they're about to release it. Or that it won't take a few months to figure out what's causing it.)
The "when is x going to be released" question is one of the most frequently asked ones here - and the one that can't be answered until the release. (And sometimes not even then - at least 2 releases have been withdrawn in the past 12 months that I can recall - after they were already being sent out.)