What does ‘we take our last customer 30 minutes prior to close’ mean?

We run our business within a set time of day.  Malls require us to maintain operating to posted times and not to exceed those times, we can incur fee's due to late operating hours.  For our stand-alone shops, we also try to maintain a strict operating schedule.  We are not a national chain and run off first come first serve, unless an apointment has been made.  We are a small, 2 chair neighborhood barbershop. We are first come, first served with no appointments. We aim at seating our last customer 30 minutes prior to close. Sometimes we may stop taking people hours prior to closing time based on how many people are waiting. We have no control over who comes when, so get here early.