code: public static void setDefaultTimezone(final String tzname) {
      final TimeZone tz = DateTime.timezones.get(tzname);
      if (tz != null) {
        TimeZone.setDefault(tz);
      } else {
        throw new IllegalArgumentException("Invalid timezone name: " + tzname);
      }
    }
docs: Sets the default timezone for this running OpenTSDB instance
  <p>
  <b>WARNING</b> If OpenTSDB is used with a Security Manager, setting the default
  timezone only works for the running thread. Otherwise it will work for the
  entire application.
  <p>
  @param tzname Name of the timezone to use
  @throws IllegalArgumentException if tzname isn't a valid timezone name