I had the same problem xoops 2.2. When my users registered, I did not allow them to set their time zone. So you need to set the default time zone. Log in as ADMIN for our site... go to Administration, Modules, Extended Profiles, select fields from the menu. Look down the list of fields for one named "timezone_offset", on the right select edit. Set the time zone for your user/members that will be adding content to the calendar. Now all that register from this point will have the right time zone. You need to go edit the profiles of the members that already signed up.
Another place to look.
Login as ADMIN, look at Preferences, System, General Settings.

Here, put this in a folder on your server and run it from a web browser. It will give you the server time.
time.txt
right click---save as you know the drill
Rename the file ..like...time.php
http://www.yourserver/folder/time.php