My office does not have set hours, except to be in no later than 9:30 "most" days. I usually arrive between 9:15-9:30, along with the majority of the people in the office, the time I leave varies depending on how much work I have. I also always log in on the evenings and weekends to check e-mails and deal with any issues. Lunch is almost always taken at my desk, but occasionally I will eat out with my boss or with colleagues on a Friday.
I love that we do not have set hours or a set lunch break, and that my work seems to be full of night owls! Everyone works hard and puts in, on average, far more than 40 hours a week, so they don't see the need to define our hours. (Except for our admin assistant/receptionist, who has set hours of 9:30-5:30 but always works later.)