code: public static function DATETIMENOW()
      {
          $saveTimeZone = date_default_timezone_get();
          date_default_timezone_set('UTC');
          $retValue = false;
          switch (Functions::getReturnDateType()) {
              case Functions::RETURNDATE_EXCEL:
                  $retValue = (float) Date::PHPToExcel(time());
  
                  break;
              case Functions::RETURNDATE_PHP_NUMERIC:
                  $retValue = (int) time();
  
                  break;
              case Functions::RETURNDATE_PHP_OBJECT:
                  $retValue = new \DateTime();
  
                  break;
          }
          date_default_timezone_set($saveTimeZone);
  
          return $retValue;
      }
docs: DATETIMENOW.
  
  Returns the current date and time.
  The NOW function is useful when you need to display the current date and time on a worksheet or
  calculate a value based on the current date and time, and have that value updated each time you
  open the worksheet.
  
  NOTE: When used in a Cell Formula, MS Excel changes the cell format so that it matches the date
  and time format of your regional settings. PhpSpreadsheet does not change cell formatting in this way.
  
  Excel Function:
  NOW()
  
  @category Date/Time Functions
  
  @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
  depending on the value of the ReturnDateType flag