The setting under Account Expiration determines if the user account should be set to be deactivated after a set date.
Note:
Changes to the user's page are not saved until you click Save.
Note:
This option is disabled for the Administrator and Manager user accounts.
To set an account to expire, enable the Automatically deactivate this account after a certain date setting. After that setting is enabled, a date selection field is displayed. Enter the last day that the account should have access in the Deactivate Account After field. The current date is displayed by default.