We are talking about the release date of the actual thing, not the alpha. Relic have not announced when it will be released, but we are just speculating as D-Day would make sense to tie in with the Western Front.
Hm I think thats rather unlikely, since its too early.
Amazon.com has the 25. and Amazon Germany the 27. as a release date. Im not saying that amazon knows it all, but those dates are more realistic in my opinion.
Relic wants to invite people to the alpha in waves and the alpha isnt even released yet. And gathering information and implementing the necessary changes until an alpha becomes a full game will probably take longer than ~3 weeks