BUG REPORT It is not safe to rely on the system's timezone settings.

[Felix]

I had this error message thrown from my local development server
The solution was to open php.ini and search for "data.timezone"
Uncomment data.timezone
and example set it to this: data.timezone = "Europe/London"

change "Europe/London" to your local time zone

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Go to your hosting CPanel and see if you can edit php.ini
and check if data.timezone is configured

If your CPanel does not give you the option to edit php.ini
then create your own php.ini and upload it to the root
of your website.

See if that helps