We like where you are going on this.  If you'd consider adding a new "time slot" option.  AM/PM.  We do not use hours, you either have an AM appointment or PM.  We can each take 3 appointments max for each slot (but this can be variable, so I'd say keep using the max feature you have now).  We also saw you plan to add detail appointment info to the day display.  This is good, as we need to see this.  The pop-up is messy, maybe we don't understand the formatting. It also reports an "undefined title". Our workers WILL NOT log into wordpress, but the site is private, so we'd need to see the details on the calendar.  Great work so far!