Yeah... my own setup for a hobby project of mine renew 30 days in advance but I don't think the way it is set up will try again tomorrow if it fails today.
i also have a daily cron. One of the renewals somehow repeatedly reissued the cert for 5 consecutive days without me noticing. For some reason the certificate was also nowhere to be found, and letsencrypt woulnd't let me manually renew the certificate because it had exceeded the limit of 5 issuances/month (or something of that sort). Thankfully the limitation is only for the exact same cert, so you can issue a new one for a slightly different set of domains without waiting for the period to pass.
With certbot, the check to see if certificates are close to expiry is done offline. So the service is only hit if a renewal is needed. The developers of certbot actually recommend that you schedule the cron twice a day.
EDIT: Actually I'm wrong. It also checks if the certificate was revoked via OCSP. However I can't imagine that it consumes much resources.