Another site using Let's Encrypt, this blog! The certificates are good for 90 days from Let's Encrypt and I was able to get the certificate in a few minutes. I also setup a cron job to automatically check all of the certificates every morning to see if any can be renewed, so they might as well last forever. Feels good man.
This is something I ran into another time, but after getting the certificate my site still wasn't locked with the "Secure" badge next to the address. I was using Amazon S3 to serve the images for the site (as I'm using here) and there was a mixed content warning. It turns out in Craft CMS, all you have to do it update your asset sources in the admin to "https://......". Luckily that was it. For these simple sites it's easy because you're not pulling in anything from an 'unsecure' source, just YouTube videos and assets from S3.
I followed the certbot guide from Let'sEncrypt.com's documentation and it was super easy. It took me much longer to write this post than it did to get the certificate to secure keiith.com. 10/10 will use again.