"Oh, not at all," Snape parried coldly. "I assure you, day or night, there are no duties more important than monitoring the security of this school. I'm sure you understand that only a severely restricted set of individuals are able to enter and exit through Hogwarts' defenses. The fact that anyone - much less a pair of duly sworn-in Hogwarts professors - sought entry at dawn... well, I could hardly have ignored such an unconventional event." The last two words were positively growled; the sound leaves no doubt that Snape looked anything but unkindly upon such a disturbance of his rest.