How does SSL It! extension renew certificates?
Let’s Encrypt SSL certificates have a validity of 90 days.
SSL It! extension has a scheduled task named
keep-secured.php visible in Tools & Settings > Scheduled Tasks.
This task run hourly and renew certificates which are soon to be expired (< 30 days).
Note: It is also responsible to issue a certificate automatically if Keep websites secured with free SSL/TLS certificates option is selected in Service Plans > plan_name > Additional Services or in Domains > example.com > SSL It!.
These tasks can be disabled following the article Is it possible to disable Let`s Encrypt certificate renewal?