VW HQ give the build dates... If they haven't given your order a slot in production, then they won't tell your dealer a date, so they won't be able to give you a date.
It also depends on what options your ordering on the car. Obviously a Silver or Black car with just simple options like 18" wheels and DSG are gonna be more readily avaliable (possibly even built somewhere already) than a car with a huge spec sheet like ACC, Sat Nav, Leather, Luxury Packs etc....