The calendar page is the live adjusted default time (UTC), the calendar island is a cached based on the Public Calendar's "Portal Cache Settings" within the Control Panel (its stored so multiple hits to every page don't send un-needed requests to the database).
Missouri is -6 GMT (Central Time Zone), so at about 6 PM you'll see UTC hitting midnight.
The forum default timezones and time data are all admin side, so there isn't anything a user could really do to make changes.
It is currently almost noon PST and the date in the calendar here is still the 18th, as expected.
