2
You set the site timezone in system admin -> preferences -> general settings
The date format is set in xoops_root/language/[yourlanguage]/global.php - in the
define("_DATESTRING","Y/n/j G:i:s");
define("_MEDIUMDATESTRING","Y/n/j G:i");
define("_SHORTDATESTRING","Y/n/j");
around line 160