code: public static function setDefaultTimezone($timeZone)
      {
          if ($timeZone = self::validateTimeZone($timeZone)) {
              self::$defaultTimeZone = $timeZone;
  
              return true;
          }
  
          return false;
      }
docs: Set the Default timezone to use for dates.
  
  @param DateTimeZone|string $timeZone The timezone to set for all Excel datetimestamp to PHP DateTime Object conversions
  
  @throws \Exception
  
  @return bool Success or failure
  @return bool Success or failure