Timezone, hours and session types to set first
Set the timezone the practice works in first, because everything the client sees is written in it. Enter each consultant with the hours they will actually take clients and the notice they need. List your session types with honest durations, and add the preparation and write-up time you really need rather than the amount you would like to need. Decide the length of the intake call and how much of the week it may occupy. Write your cancellation notice and what a late cancellation means. Decide who may book on a consultant’s behalf, and where the meeting link for an online session comes from. Then publish a narrow window before a wide one: it is easier to open more hours than to take them back.
Where this client booking system stops
The session is the product here; the work around it belongs elsewhere.