These settings are found at:
Configuration -> System Setup -> Scheduling
Prevent Make-up Bookings x Minutes before Class Start Time
Allows you to apply a cut-off time for make-up bookings so that you have ample notice of a booked make-up lesson in a class.
This setting can be configured for any amount of time you desire, in minutes.
For example, if you want to prevent any make-ups being booked in 2 hours prior to a Class Start Time, you would enter 120 in this field setting. Then even if there is make-up availability, Classes with a start time within this window would not display for available make-ups.
A value of 0 or an empty field will allow make-up bookings up to the Class Start Time.