Source — /etc/systemd/system/timers.target.wants/certbot.timer

/etc/systemd/system/timers.target.wants/certbot.timer

[Unit]
Description=Run certbot twice daily

[Timer]
OnCalendar=*-*-* 00,12:00:00
RandomizedDelaySec=43200
Persistent=true

[Install]
WantedBy=timers.target