As per this article https://support.atlassian.com/organization-administration/docs/manage-an-organization-with-the-admin-apis, the admin key can last from a week up to a year. Currently, no email notification is sent when the key expires or is about to expire.

The suggestion is to send a reminder notification to the organization admins some time prior to the expiry date. This can be very useful to avoid any issues that may arise due to an expired key.