把下列代码复制到想放置的位置,例如 footer.php(自行修改起始时间)

<span id="runtime_span"></span>
<script type="text/javascript">function show_runtime() 
    {
        window.setTimeout("show_runtime()", 1000);
        X = new Date("3/2/2020 00:00:00"); Y = new Date();
        T = (Y.getTime() - X.getTime());
        M = 24 * 60 * 60 * 1000; a = T / M;
        A = Math.floor(a); b = (a - A) * 24;
        B = Math.floor(b); c = (b - B) * 60;
        C = Math.floor((b - B) * 60);
        D = Math.floor((c - C) * 60);
        runtime_span.innerHTML = "网站已运行" + A + "天" + B + "小时" + C + "分" + D + "秒"
    } show_runtime();
</script>

效果如图: