经测试代码如下：
<!DOCTYPE html>
<html>
<head>
<Meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
.leave_time_font{margin-left:35%;}
#fo{margin-left:32%;}
</style>
<title>js网页倒计时</title>
</head>
<body>
<h1>WoYaoNi.CN </h1>
<script src="./jquery.js"></script>
<script type="text/javascript">
/**
* 倒计时，精确到秒级
*
* @param
* @arrange (512.笔记) jb51.cc
**/
$(document).ready(function(e) {
var _countSeconds = 0;
function _countDown(){
_countSeconds ++;
$('input.surplustime').each(function(index,element) {
var $this = $(this);
var _totalTime = Number($this.val()) - _countSeconds;
var _day = parseInt(_totalTime/86400);
var _hours = parseInt(_totalTime%86400/3600);
var _minutes = parseInt(_totalTime%86400%3600/60);
var _seconds = parseInt(_totalTime%86400%3600%60);
var _strLite = '<span class="day">'+_day+'</span>天<span class="hour">'+_hours+'</span>小时<span class="minutes">'+_minutes+'</span>分<span class="seconds">'+_seconds+'</span>秒';
var _str = '倒计时：'+_strLite;
if($this.next('p.daojishi').length > 0){
$this.next('p.daojishi').html(_str);
}else if($this.next('p.leave_time_font').length > 0){
$this.next('p.leave_time_font').html(_strLite);
}
});
}
setInterval(_countDown,1000);
})
</script>
</head>
<body>
<?PHP
ini_set('date.timezone','Asia/Shanghai');
$currenttime = time();
$a = strtotime('2014-2-14 00:00');
$b = $a-$currenttime;
?>
<div id="djs">
<div id="fo">小伙伴们距离情人节只剩：</div>
<input type="hidden" name="surplustime" class="surplustime" value="<?PHP echo $b; ?>" />
<p class="leave_time_font"><span class="day">0</span>天<span class="hour">0</span>小时<span class="minutes">0</span>分<span class="seconds">0</span>秒</p>
</div>
</body>
</html>