<?php

$commentsArray = [['comment'=>'blabla1', 'time'=>time()-3600],
	['comment'=>'blabla2', 'time'=>time()-7200],
	['comment'=>'blabla3', 'time'=>time()-3100]];
$i = 0;
foreach ($commentsArray as $arr) {
	$comments[$i] = $arr['comment'];
	$times[$i] = $arr['time'];
	$i++;
}

array_multisort($times, $comments);
echo "<pre>", print_r($comments, true), "</pre>";

?>