I believe there is a start time issue in your application.  When I schedule a 1-hour appointment to start at 8:00 am and then a following 30-minute appointment that works fine the 8-9 hour block is grayed out and I can only access the slot starting at 9 to 9:30.  However when I schedule a 1-hour appointment starting at 8:00 and then try to schedule a 45-minute appointment right after the first available slot is 9:30 NOT 9:00.   I have 1 location, 1 worker, and 3 connections set up (60 min appointment, 45 min appointment, 30 min appointment).  Under settings/Customize I have Multiple work unchecked.   Thanks for the help