@julian I'm still determining what is best. I think once a month depending on the timing could be problematic (although a manual renew isn't the worst thing in the world).
Even the letsencrypt walkthrough says twice a day
Note: if you're setting up a cron or systemd job, we recommend running it twice per day (it won't do anything until your certificates are due for renewal or revoked, but running it regularly would give your site a chance of staying online in case a Let's Encrypt-initiated revocation happened for some reason). Please select a random minute within the hour for your renewal tasks.
I might go with that or I might go weekly. We'll see.