将以下代码插入到主题中的 functions.php 文件中

function  art_count ($cid){
    $db = Typecho_Db::get ();
    $rs = $db->fetchRow ($db->select ('table.contents.text')->from ('table.contents')->where ('table.contents.cid=?',$cid)->order ('table.contents.cid',Typecho_Db::SORT_ASC)->limit (1));
    $text = preg_replace("/[^\x{4e00}-\x{9fa5}]/u", "", $rs['text']);
    $text_num = mb_strlen($text,'UTF-8');
    $read_time = ceil($text_num/400);
    $output = '本文共' . $text_num . '个字,预计阅读时间需要' . $read_time  . '分钟。';
    return $output;
}

在需要引用的地方插入如下代码

<?php _e(art_read_time($this->cid)); ?>