On 15 Jun 2019 at 05:15p, Michael Batts pondered and said...
 
 MB> To stay on topic; What is the Mystic Time Zone Environment Variable used
 MB> for? How is it set?

It's usually picked up by the variable being set in the OS.
You see it used as a kludge line in echomail amongst other things.

--- Mystic BBS v1.12 A43 2019/03/03 (Windows/32)