Response headers from mls2atx.com indicate that WordPress was installed by October 4th, 2017 at the latest.
The css file “http://mls2atx.com/wp-content/themes/Avada-Child-Theme/style.css?ver=4.8.3” contains a “last modified date” of Wed, 04 Oct 2017 16:34:27 GMT
Pictorial evidence of the response headers has been documented.
Thanks to @knass for digging through these records and making this discovery.