There's a chance that you'll see a price drop by the Xbox One's release (Nov. 22), but that's completely based on the idea that with the release of the next gen console, Blacklist will have lost a bit of the hype around it.
But that's just pure speculation. For all I know, the game will hold its value, long into the holiday season.
There's no official time listed that I know of. Like most games, you can expect it go down in price once the hype starts to diminish. Because it's a more popular game, it will likely stay close to the same for a while (while games that don't sell
well to begin with often drop in price much more drastically).
You can likely go and get a used copy for a reduced cost now, though reduced by how much is up to the seller.