Let's Encrypt renews certificates after 60 days by default, giving you a 30-day grace period for outages, etc. Use a daily cronjob and monitor your certificates

Let's Encrypt renews certificates after 60 days by default, giving you a 30-day grace period for outages, etc. Use a daily cronjob and monitor your certificates. Setup alerts if your certificates are closer than, say, 25 days to expiration. This should cover temporary outages, bugs, etc. - and the monitoring bit is no different from what you should already have even with manual renewal.