As the article says, you need to work with your webserver administrator to find the correct resolution.

"Error 500 - Internal Server Error" is a GENERIC response triggered by the server BEFORE Zen Cart can operate. So you need to work with the people who have access to the configuration components of the server that fire before Zen Cart is involved. And that means the webserver engine (apache and configs) and filesystem (files, file permissions, etc).

And the error message you quoted is talking about a PHP misconfiguration ... where the server's master PHP configuration doesn't have a timezone set in it. Again, the webserver top-level administrator has the access required to set that correctly in a way that prevents EVERYONE on the server from getting that error message.