In Appointment Book, if you want to change an operatory's scheduling for a specific day - e.g., open a closed op; close an open op; change the hours for an op from all day to 1/2-day, etc. - you right-click the operatory header and choose "Operatory Setup...". That opens the tiny "Operatory Setup" window. If you choose the operatory you want to change, the hit the "Schedule" button, that opens the "Schedule Calendar for <operatory name>" window. If you navigate to the date in question and then choose the top left menu option called "Reset Hours for Selected Date", nothing happens. I would think that would open a dialog box where you have the options to either close the op, open the op and/or alter the hours for that op on that specific date. See the attached photo with annotations. This appears to be a feature of the software that is broken and needs to be repaired.