Extending or shortening the validity period of root certification authority certificates
With existing public key infrastructures, you may find that the validity period of the root certification authority certificate has not proven itself. For example, it could be that it was chosen too short (the default setting of Microsoft AD CS is only five years), or even too long, which may not be optimal from a security perspective.
If you renew the certification authority certificate, you may want to achieve a different validity period.