In some cases, answers are in the questions. Just think about it. If there was no need to work night shifts, employer would never ask you about such option.
Twelve-hour long shift and working in the night is anything strange for the receptionist. Each job has some pluses and some minuses. You should say more than just, “I can work night shifts.” To make a good impression, try to elaborate on your “yes” with further explanation. Let me show you an example:
I can definitely work during the night. I do not have children, so there is no reason for me to sleep home at night. I am flexible and count with this option.
I would not mind working twelve hours a day. In my previous job it was not uncommon that I worked even fourteen hours a day sometimes, when a colleague got sick. I can stay focused for a long time periods of time without getting tired.