Site.getTimeZone ()
function returns the (already cached) TimeZone-Object according to site-preferences

Sourcecode in Site/objectFunctions.js:
1:   function getTimeZone() {
2:      var tz = this.cache.timezone;
3:      if (tz)
4:          return tz;
5:      if (this.preferences.getProperty("timezone"))
6:          tz = java.util.TimeZone.getTimeZone(this.preferences.getProperty("timezone"));
7:      else
8:          tz = root.getTimeZone();
9:      this.cache.timezone = tz;
10:     return tz;
11:  }