The book's been released. You don't have to wait until May. if you don't wish to. But then you may have ordered it just recently and so it will take awhile? I got mine quickly because I immediately pre-ordered on Amazon, when you announced on this forum that the book was coming out.
I mostly have good interaction with Amazon myself, but I guess because Richard and I order so frequently, there's been little mishaps here and there over the years (mostly very slow delivery -- it once took a MONTH to get a vintage issue of Opera News, and these dealers were right here in Pennsylvania. I know it was because they didn't get up off their duffs and put the thing in the mail. One would think the magazine was delivered by pack mule.)
Give 'em a little nudge if Bix doesn't show up on your expected May delivery date.