<html>
<body>
<form action="" method="POST"><textarea name="dates"></textarea><button type="submit"> Gönder </button></form>
<?php if($_POST){?>
<?php foreach(explode("\r\n", $_POST['dates']) as $date){
$strtotime = date('Y-m-d',strtotime($date));
$dates[strtotime($strtotime)] = $date;
}
ksort($dates);
echo implode('</br>',$dates);
} ?>
</body></html>