public function format($value)
 {
     if (empty($value)) {
         return null;
     }
     $time = XlsxDateTimeUtils::toTime($value);
     return "<c r=\"cellAddress\" s=\"7\"><v>{$time}</v></c>";
 }
 public function format($value)
 {
     if (empty($value)) {
         return null;
     }
     $date = XlsxDateTimeUtils::toDate($value);
     $time = XlsxDateTimeUtils::toTime($value);
     $timestamp = $date + $time;
     return "<c r=\"cellAddress\" s=\"8\"><v>{$timestamp}</v></c>";
 }