Depending on the position you are applying for, there might be rotating shifts, or evening and weekend hours as well. They're gauging your overall flexibility and expectations, and how well your answer to this question aligns with your other answers provided through the interview set.

Best to be honest. If you have other priorities or demands on your time that aren't conducive to working lots of overtime or covering other shifts, then it is worth clarifying this now. It is better for both an employee and an employer to learn that the job isn't a good fit earlier rather than later.