It depends on your stave. You should make any corrections with heat before you add a rawhide backing. Other than that before you begin stressing the bow, so after floor tiller. I have tillered bows all the way before adding rawhide but usually the only reason to add any backing is if the back ring is violated, thin ringed or has knot problems.
I use the same method for both snake skins and rawhide. actually they are both rawhide anyway. Pat