I'm leaving open the possibility that my info is wrong here, but I'm pretty sure Williams could sign early if he wanted, he just can't enroll early. Not that it really matters, because he isn't.
On another note though, if you're the type that tends to worry and get worked up about every story and rumor that bubbles up on a key recruit like this, I'd suggest enforcing your own blackout coverage on him until he finally puts pen to paper.