At any point. I only know of 2 dealers that do near invoice as policy. Some dealers, it depends on whether or not they are in a good mood when you walk in.
Please remember, Raptor availability is based on allotment. In other words, Mother Ford dictates how many Raptors a dealership can sell. So if a dealership is only allotted 5 Raptors every year than they will maximize their profit by selling them as high above MSRP as the market will support.
The two dealers near you that do that, are they big volume dealers on SVT products? It makes a lot of sense if certain dealers are allotted say 5 raptors a year. But, I wouldn't go to someone like that. The local dealer here is the number one dealer in Canada and he told me customers can come in and order a Raptor whenever they become available.