you can order 1,2, or 3 pistons from them. You get charged alot more and you're better off buying 4 because then they give you the same price per piston as if you were buying 8.
My first set of pistons were machined too much for rod clearence and if it were n/a it'd been fine but the first hit of the button with my setup and they would be ashtrays. I got them sent back and had another set made and expedited the same week and wasn't charged the expedite fee, so I cant complain about time. But if you look they are about the most popular piston out and if they can't get you one by Thursday it might be because they have soo many orders?