Hi,
You can use Venue feature of OS Services Booking to disable booking in a time period from now.
With Venue feature, you can setup "Disable dates before" by hours, dates ..etc. By this way, you can prevent customers from booking on your timeslots before X (days, hours) from now.
To add Venue into your Booking system, you need add new Venue, in Venue modification form, you should select Services which are placed in this Venue.
Next step, when you assign Employee to Service, if the Service is placed in more than one Venue, you should select Venue that the Employee will work on.
Lastly, when you setup menu to layout: OS Services Booking - Default layout, you need to select Venue from parameter: Venue in Menu parameters form.
You should implement all steps to make the feature of Venue to be applied to your Booking system.
Thanks
Dam