Greetings,
OS Service bookings uses a substractive/reductive approach to creating available timeslots. Using this diagrams with the accompanying notes will help you set or troubleshoot any time slot problems.
The top level of the diagram is the coarse level and the further you go down the more you are refining the available timeslots for a specific employee.
Let me know if this helps. If you wish to improve it, contact me an I will send you the original word doc.
PS I have created a post specifically for "Custom timeslots"
Ray