If you want to limit how far in advance clients must book an appointment (to prevent last-minute or same-day bookings), you can do this using the Latest Appointment/Class setting found in the Service & Class Time Display panels (which can be found by going to Settings > Time > Service Time Display or Class Time Display). The default setting for your account gets decided on these panels -
The Latest Appointment/Class setting determines how much advance notice is required for clients to book an available timeslot. It prevents clients from seeing or booking any timeslots that fall within that cutoff window.
Customizing for Specific Services or Classes
You can also customize this setting on a per-reason basis on the Time page of each service or class profile. Adjusting this setting on the reason profile will disconnect this option from updating with the account's default and allow you to set a different Latest Appointment range for each booking option.