I remember that Snow Leopard wasn't even released in the month they announced, but the one before.
Final Cut pro X, however, was released at the end of the month.
There's nothing too notable about Apple releases: I think that they don't know either, they will delay it if they find an unexpected bug, and they have a "security window" to allow for such delays, but the bugs might be bigger than expected, too, and might take longer to fix than they expect.
I also think that they won't care about minor bugs here, as we know, .0 releases are full of bugs and Apple even knows about them.
So yeah, all I can say is we don't and can't know just from past releases. Could be anytime now!