We use "Let’s Encrypt" and "cPanel Comodo" SSL Certificate providers that instantly issue SSL to domain name by Domain-Validated (DV) process. The maximum duration for free SSL is 90 days, this cannot be changed but we have an automated program that will automatically renew your SSL certificate 3 days before expiry. This automated renewal process has been configured into cPanel's AutoSSL feature.
For more details about SSL Certificate validity visit:
https://letsencrypt.org/2015/11/09/why-90-days.html