I cannot advise you on tall fescue. Most grass seed will remain dormant when it is too cold, although they may absorb water. I feel that they will begin to grow--but slowly--in the spring when soil temps hit the proper range, rather like what happens in nature. My opinion, is that a dry spell just after seedling emergence, is the biggest risk.
In my experiments on new rye seedlings placed into freezers...I saw that the area of rapid growth about a half-inch above the soil was most affected. That area turned brown and new grass bent over at the half-inch point.