将代码放入functions.php

一般在主题根目录:网站/usr/themes/主题

// 设置时区
date_default_timezone_set('Asia/Shanghai');
/**
 * 秒转时间，格式 年 月 日 时 分 秒
 *
 */
function getBuildTime() {
    // 在下面按格式输入本站创建的时间
    $site_create_time = strtotime('2021-06-23 00:00:00');
    $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'
        .$value['seconds'].'秒</span>';
    } else {
        echo '';
    }
}

修改 footer.php

在页脚选择合适的位置加入:

<?php getBuildTime(); ?>