April 22nd - June 10th 2014. Unless something goes really bad. Anything later than June without a major patch to hold us over (or giving EVERYONE free beta access) would be big trouble.
There aren't going to hit 12 or 18 months, but I do believe they are capable of 20-22 months. I wouldn't be at all surprised to see beta starting in early January. I really doubt they'll do it before Xmas though.