code: public static function setTimeZone($timezone)
      {
          if (self::validateTimezone($timezone)) {
              self::$timezone = $timezone;
  
              return true;
          }
  
          return false;
      }
docs: Set the Default Timezone used for date/time conversions.
  
  @param string $timezone Time zone (e.g. 'Europe/London')
  
  @return bool Success or failure