Clarification on when you can enter AQ40

[Superfragger-sulfuras]

@Kaivax

Once the gong is rung on a realm, the 10 Hour War begins. Once the 10 hours has elapsed, "Bang a Gong!” can never be turned in anymore, the two Ahn’Qiraj raids will open, and the “Treasures of the Timeless One” quest will become available.

Is this proof enough? Or do you want an academic, peer-reviewed paper on the subject?