You can optionally set an expiry date on Galleries, which means the Gallery will no longer be accessible to your clients once it expires.
There are 2 ways to change the expiration date of a Gallery:
Click "Settings" in the Gallery itself, toggle the "Expires" toggle on, and set the expiration date.
Click the three dots to the right of the gallery you want to edit and choose "Set Expiration" if the Gallery isn't set to expire, or "Extend Expiration" if the Gallery is set to expire.
You can bulk-change the expiration dates of your Galleries from the Galleries List page. Click the checkbox next to each Gallery and use the "Bulk Actions" button above the column and choose either "Extend Expiration" or "Set Expiration" options.