$(document).ready(function () {

var oDate = new Date();

var nowTime = oDate.getTime(); //现在的毫秒数

oDate.setMinutes(oDate.getMinutes() + 25, oDate.getSeconds(), 0);

var targetDate = oDate;

run(targetDate);

});

function run(enddate) {

getDate(enddate);

setInterval("getDate('" + enddate + "')", 500);

}

function getDate(enddate) {

var oDate = new Date(); //获取日期对象

var nowTime = oDate.getTime(); //现在的毫秒数

var enddate = new Date(enddate);

var targetTime = enddate.getTime(); // 截止时间的毫秒数

var second = Math.floor((targetTime - nowTime) / 1000); //截止时间距离现在的秒数

var day = Math.floor(second / 24 * 60 * 60); //整数部分代表的是天；一天有24*60*60=86400秒 ；

second = second % 86400; //余数代表剩下的秒数；

var hour = Math.floor(second / 3600); //整数部分代表小时；

second %= 3600; //余数代表 剩下的秒数；

var minute = Math.floor(second / 60);

second %= 60;

var spanH = $('.se-txt')[0];

var spanM = $('.se-txt')[1];

var spanS = $('.se-txt')[2];

if(spanH!=''&&spanH!=null&&spanH!='undefined'&&spanM!=''&&spanM!=null&&spanM!='undefined'&&spanS!=''&&spanS!=null&&spanS!='undefined'){

spanH.innerHTML = tow(hour);

spanM.innerHTML = tow(minute);

spanS.innerHTML = tow(second);

}

}

function tow(n) {

return n >= 0 && n < 10 ? '0' + n : '' + n;

}

参考这个呢

https://bbs.fanruan.com/thread-133719-1-1.html