I think if you wait abit, atleast an 1 1/2 into the 3, you wouldn't lose any of the rub as it has already started to work its way into the meat too much to fall off. As the meat sweats, you would think it would drip off, maybe some does, but not much. Probably the reason you do a good dusting with the rub to begin with. When I do some fish I spray it with a 50-50 Canola Oil/Lemon mix, then pat dry with paper towel. I do get some rub on the paper towel, but not as much as you think.
If you do not want full 3-2-1 "fall off the bone" remember to adjust your times some. The more time in the foil the better chance for "fall off the bone", so maybe a 3-1.5-1.5 might be more to your taste.