Or just do what Let's Encrypt suggests and have a cron job that runs certbot-auto's renewal command twice a day, every day? It doesn't actually renew until nearing the end of the 3 month cycle, but by having two attempts per day it will make it far more likely to go through if the network is down or something otherwise prevents it from renewing one of the times. They, of course, also will email you repeatedly as you near the end if you haven't yet renewed.

Sounds like a great strategy!