In all the years I have never looked into cron.
But it is really a very straightforward functionality, which is used by Linux itself.
You can either schedule user specific jobs or use /etc/cron.d files or /etc/crontab.
There is a certificate update script --> https://github.com/HCL-TECH-SOFTWARE/domino-cert-manager/blob/main/examples/nginx/cert_upd_nginx.sh
This is a companion discussion topic for the original entry at https://blog.nashcom.de/nashcomblog.nsf/dx/linux-using-cron-to-schedule-periodic-jobs-like-certificate-updates.htm