In order to add the slot in Category:
Go to the "Category".
Click on the "Calendar Icon" under "action".
3. Click on the "Date" that you want to edit.
4. Add the "slots" and specify the pax, that indicates the maximum number of persons that can schedule an appointment during that specific time slot.
5. Click on "Apply".
You will be able to see the slots on the booking page as illustrated below: