After answering the question for the tenth time, I decided to get creative with my response. For the rest of the day, I used different combination of these words and phrases:
We're [open/keeping/closed] [regular, everyday, standard, usual, customary, typical] hoursI felt like a walking thesaurus, but I enjoyed thinking of unique ways to say the same thing over and over. When my replacement arrived, I cued him in on what to expect. I know repetitive questions really annoy him, so I figured it was the least I could do.