People argue that this can be a difficult question to answer, because you obviously can't say no, and saying yes may appear as an invitation for the company to exploit you. But if you think about it, you're bound to do overtime at one point or another. Also, depending on the nature of the work, overtime may be inapplicable because the work itself involves rendering long hours. Moreover, if you're applying for a managerial position or a position that is focused more on projects than operations, note that there may be no overtime pay, and overtime may simply be a given.

If you do not feel comfortable saying yes outright, you can sidestep by expressing your agreement or determination to deliver what is asked or needed of you. This has the additional benefit of showing you as being goal-driven rather than a clock-watcher.