php 时间倒计时

<?php
session_start();

$attr = $_SESSION["djs"];

$fen=$attr["fen"];

$miao=$attr["miao"];

if($fen==0 && $miao==0)
{
echo "over";
exit();
}

if($miao==0)
{
$attr["miao"]=59;
$attr["fen"]=$attr["fen"]-1;
}
else
{
$attr["miao"]=$attr["miao"]-1;
}

$_SESSION["djs"]=$attr;

echo "{$attr['fen']}|{$attr['miao']}";