Change order
By default the booking process will start with the "Date/Time" selection, then the "Services selection" and then the "Assistant selection".
You should enable this option if you want that the first step of the booking process for your customers is the "Services selection", then the "Assistant selection" and then the "Date/Time" selection.
We do suggest you this second order as it will present to the customers only the available date/time slots for the selected Services and Assistants combination.