Changeover days refers to the number of days after a checkout that the property will be unavailable. 

The property will only be available to book again after that length of time. It’s a useful feature if you need to prep your property in-between bookings.

To add changeover days you must follow these steps:

Go to PMS.
Choose your property.
Then click on the Settings tab.
Now, in the Availability Settings section, click on Manage.
Scroll down until you get to Calendar Settings and here you can choose your changeover days. 
Click Save.