Let's Encrypt DNS Record
If a Let's Encrypt DNS record is found, this tests the TTL for that record.
One of the most common ways to get an SSL certificate is via the free Let's Encrypt organization. There are various ways to authenticate your site with Let's Encrypt and get an SSL certificate. One of those ways is via a DNS record.
This test will check to see if that record exists and if it does, it will check the TTL for that record. If the TTL is too long, it can cause delays with renewing the certificate.