The rifles being spoke of are parts sets, not kit guns like a TC hawken or a Lyman GPR. Although I know many do refer to a parts set as a kit. If this is going to be your first rifle build, its a good idea to get some reference on the subject in the way of books, and or videos. The rifle you are speaking of does require a good bit of work and you will have a good bit more time in it than 40 hours, along with a lot of patience. Unless you have built rifles before. Even then I believe it will take more than 40 hours of work.
I never got a parts set from track, but what I've heard they do a good job. I have heard that at times it may be a long wait to get a barrel. Don't know if that is true, just what I've read. The rifles from Track are not as historically correct as some others like Chambers, but of coarse you will pay more for a Chambers parts set. There are other good suppliers of parts sets, like TVM, Dunlap, Pecatonicia River, Cabin Creek, and others. TVM will build a rifle for you complete. They will even do carving and engraving. Just depends on how much money you want to spend. They will also build the rifle as far as you want, or just sell the parts set. I have seen some of the rifles they have built, and they do an excellent job.
I'm in the process of getting a parts set from either TVM or Chambers. Just undecided yet if I want to spend the extra money for a Chambers.
A good place to find answers is the Muzzle loader forum. Lots of knowledgeable people there when it comes to building rifles.