If you would like to use the commandline to check your ssl expiry dates of website, including external websites then you can use the following:
\\
You can change lukeslinux.co.uk:443 to your website.
\\
It also works with *:443 and localhost:443
<sxh bash>
echo | openssl s_client -connect localhost:443 2>/dev/null | openssl x509 -noout -dates
</sxh>