They post the calendar for the next month on the 25th. They only have a limited number of appointments, so you'll need to check on the 25th to get an appointment slot for the next month. If there aren't any appointments it means they're already booked for the next month, unfortunately.
When there are no appointments available on the calendar it means that we are fully booked for the month. Our appointments fill up really fast. As Kasey answered, appointments for the next month (we only open one month at a time) opens up at midnight on the 25th of current month (when the 24th turns into the 25th).
Thanks! Your answer is awaiting moderation.