PHP和js实时倒计时

<?php//这是t.php页面header('content-type:text/html;charset=utf-8');date_default_timezone_set('PRC');$start_time = '09:00:00';$end_time = '18:00:00';$start_famate_time = strtotime($start_time);        //开始时间转化为时间戳$end_famate_time = strtotime($end_time);          //结束时间转化为时间戳$now_time = time();if($end_famate_time < $now_time || $start_time > $now_time){    echo "当前不在考试的时间范围内！";exit;}$remain_time = $end_famate_time-$now_time;            //剩余的秒数$remain_hour = floor($remain_time/(60*60));             //剩余的小时$remain_minute = floor(($remain_time - $remain_hour*60*60)/60); //剩余的分钟数$remain_second = ($remain_time - $remain_hour*60*60 - $remain_minute*60); //剩余的秒数echo "距离秒杀结束还有".$remain_hour."小时".$remain_minute."分钟".$remain_second."秒";?>

<div id="showTime"></div><script src='jquery.js'></script><script>    $(function(){        st();    });    var aj;    function st(){        aj=$.ajax({            'url':'t.php',            'success':function (data){                $('#showTime').html(data);                aj.abort();//销毁上一次ajax对象                st();            }        });    }</script>