Be honest. If you really want the job and are willing to work any schedule needed, say so. If, however, you have no intention of working late hours or weekends, simply let the interviewer know the hours that you are available to work. The same applies to extra hours. You are more likely to be hired if you are willing to work any time you are needed. However, saying that you are willing and then complaining about the hours once you start working is a recipe for disaster.