I'd wait a little longer to get a better idea of how far back the limbs are dead.

As I mentioned before, the sap may have frozen under the bark. This has indeed happened to my mothers 'waterfall' (but not my trees since they were in garage), and limbs up to finger size have been completely blackened on the tops and sides.

However, it is still difficult to tell exactly the extent of the damage so I would hold off a little longer to prune hardened wood.