到固定时间才可以点击按钮

懒得解释了 直接贴代码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>index</title>
    <script src="__PUBLIC__/jquery-2.1.1.min.js"></script>
</head>
<body>
<input type="button" id="btn" value="秒杀" disabled="true"/>
</body>
<script type="text/javascript">
$(function(){
    var stringTime = "2017-04-27 19:44:00";
    var timestamp2 = Date.parse(new Date(stringTime));
    timestamp2 = timestamp2 / 1000;  //获取到的 格式日期 的时间戳

    var myDate = new Date();
    var timestamp = myDate.getTime()/1000;  //当前时间戳 获取的时间戳为毫秒 需除1000
    timestamp = timestamp.toFixed();

//过了某时间 直接不可点
var stringTime3 = "2017-04-27 21:00:00";
var timestamp4 = Date.parse(new Date(stringTime3));
timestamp4 = timestamp4 / 1000;  //获取到的 格式日期 的时间戳
if(timestamp>timestamp4){
    alert('活动已结束');
    return;
}

if(timestamp>timestamp2 && timestamp<timestamp4){
    $("#btn").val("秒杀").removeAttr("disabled");
    return;
}



var count = timestamp2 - timestamp;

var countdown = setInterval(CountDown, 1000);
function CountDown() {
    $("#btn").val("离活动开始还有" + count + "秒");
    if (count == 0) {
        $("#btn").val("秒杀").removeAttr("disabled");
        clearInterval(countdown);
    }
    count--;
}

});

</script>
</html>

可搭配 http://www.cnblogs.com/zyjfire/articles/6775383.html 食用

既不回头，何必不忘；既然无缘，何须誓言；今日种种，逝水无痕；明夕何夕，君已陌路；