I'm not sure about the first-party Let's Encrypt client, but letsencrypt.sh will check the dates and not bother to ask for a new certificate if the sertificate

I'm not sure about the first-party Let's Encrypt client, but letsencrypt.sh will check the dates and not bother to ask for a new certificate if the sertificate expires more than 30 days into the future. This way, if the Let's Encrypt servers are overloaded that day and not renewing certificates, the client will try once a day for a month before the certificate expires.