The sandbox duration must be set as minutes at the “Sandbox duration” entry of the plugin.
A countdown will be shown to the user in order to inform him/her about the time left until the sandbox expiration.
When the sandbox expires all the data related to it (user, images, contents and settings) will be permanently deleted.
All the sandboxes can be removed manually by clicking on the “Delete Sandboxes” button that you find in the plugin settings dashboard.
Consider this action carefully: by deleting the sandboxes, all the users who are using them will be disconnected and will need to create a new sandbox again.