代码部署:打开并把代码放到functions.php中即可。(注意:修改代码中的建站时间为你自己的)

参考本站及博客。
// 运行时间
// 设置时区
date_default_timezone_set('Asia/Shanghai');
/**
* 秒转时间,格式 年 月 日 时 分 秒
*
* @author Roogle
* @return html
*/
function getBuildTime(){
// 在下面按格式输入本站创建的时间
$site_create_time = strtotime('2020-02-28 08:00:00');
$time = time() - $site_create_time;
if(is_numeric($time)){
$value = array(
"years" => 0, "days" => 0, "hours" => 0,
"minutes" => 0, "seconds" => 0,
);
if($time >= 31556926){
$value["years"] = floor($time/31556926);
$time = ($time%31556926);
}
if($time >= 86400){
$value["days"] = floor($time/86400);
$time = ($time%86400);
}
if($time >= 3600){
$value["hours"] = floor($time/3600);
$time = ($time%3600);
}
if($time >= 60){
$value["minutes"] = floor($time/60);
$time = ($time%60);
}
$value["seconds"] = floor($time);
 
echo '<span class="btime">'.$value['years'].'年'.$value['days'].'天'.$value['hours'].'小时'.$value['minutes'].'分</span>';
}else{
echo '';
}
}
 在合适的位置(footer.php)调用
已稳定运行:<?php getBuildTime(); ?>
另外一种方法:
<script>
function secondToDate(second) {
    if (!second) {
        return 0;
    }
    var time = new Array(0, 0, 0, 0, 0);
    if (second >= 365 * 24 * 3600) {
        time[0] = parseInt(second / (365 * 24 * 3600));
        second %= 365 * 24 * 3600;
    }
    if (second >= 24 * 3600) {
        time[1] = parseInt(second / (24 * 3600));
        second %= 24 * 3600;
    }
    if (second >= 3600) {
        time[2] = parseInt(second / 3600);
        second %= 3600;
    }
    if (second >= 60) {
        time[3] = parseInt(second / 60);
        second %= 60;
    }
    if (second > 0) {
        time[4] = second;
    }
    return time;
}
</script>
<script type="text/javascript" language="javascript">
function setTime() {
    // 博客创建时间秒数,时间格式中,月比较特殊,是从0开始的,所以想要显示5月,得写4才行,如下
    var create_time = Math.round(new Date(Date.UTC(2013, 4, 22, 0, 0, 0))
            .getTime() / 1000);
    // 当前时间秒数,增加时区的差异
    var timestamp = Math.round((new Date().getTime() + 8 * 60 * 60 * 1000) / 1000);
    currentTime = secondToDate((timestamp - create_time));
    currentTimeHtml = currentTime[0] + '年' + currentTime[1] + '天'
            + currentTime[2] + '时' + currentTime[3] + '分' + currentTime[4]
            + '秒';
    document.getElementById("htmer_time").innerHTML = currentTimeHtml;
}
setInterval(setTime, 1000);
</script>
网站运行:<span id="htmer_time" style="color: red;"></span>