怎樣用php實現兩個時間相減，得到相差的天數

<?php
$time1 = mktime(10,20,30,2,5,2000); //2000-2-5 10:20:30
$time2 = mktime(18,30,20,5,2,2000); //2000-5-2 18:30:20
$diff = (int)(($time2-$time1)/(24*3600));
echo "$time2 和 $time1 的時間差爲：" . $diff . "天<br>";
?>