You can optionally set an expiry date on Galleries, which means the Gallery will no longer be accessible to your clients once it expires. To change the expiry date of a Gallery, select the Settings button and then go to the "Availability" tab while editing a Gallery.

You can turn on the "Expiration" toggle and choose a date for the Gallery to expire (the default is 30 days), or you can turn the toggle off to create a Gallery without an expiry date, making it available indefinitely.