There were German generals who didn't believe they could make that kind of time, and they were correct. As I am.
As I said, the Wehrmacht knew it was hopeless. They didn't
prosecute the attack to fail , necessarily but they didn't exactly fight too hard to achieve a victory. As I said many German generals felt it was more important to concentrate all that armor in the East to try and hold off the Russians for as long as possible. Hitler himself was hoping that the attack would cause a political fallout in the tenuous coalition and cause a stalemate.