I think there is more that we have to know, here..
I can think of a couple of things that could cause what you discribe
1.... this is the hen's first time hatching.. still unlikely, rare..
2.....all the eggs were not set at the same time.. actually my first guess
the older poults would leave the nest if the mother was still trying to hatch more eggs..
once the eggs hatch the adult bird never goes back to the nest..so as a result, neither do the babies..
they might go to a spot to spend the night, though.. by co-incidence it might be the nesting box..
my personnal experience is that turkeys are excellent mothers..