Being flexible with the schedule you are willing to work is always a plus. However, many people work more than one job or have a one parent home which requires them to have a flexible schedule. Others simply prefer to work one shift rather than another. Being upfront with the interviewer about what schedule suits your preference could help prevent conflict later on. It is easier to plan a schedule you can agree on than it is to fix problems that arise due to fear of being rejected. Be honest and direct.
"I am not married and have no children at this time. So, I am pretty flexible with my schedule. If I had a choice, I would prefer the late shift, as I am a bit of a night owl. However, I am excited about the opportunity to become a part of this team and am willing to work where I'm needed."
"I am open to working any schedule where I am needed. I am very excited to become a part of an organization and become established."
"Yes, I am prepared to work that type of schedule. My family and I always plan special events around my work schedule. Also, part of us giving back has always been that I like to offer to work some extra time for those who have small children or other responsibilities."