limour-blog.github.io/source/theme-inject/timeliness.js

(function() {
    var times = document.getElementsByTagName('time');
    if (times.length === 0) { return; }
    var posts = document.getElementsByClassName('post-content');
    if (posts.length === 0) { return; }
  
    var pubTime = new Date(times[0].dateTime);  /* 文章发布时间戳 */
    var now = Date.now()  /* 当前时间戳 */
    var interval = parseInt(now - pubTime)
    /* 发布时间超过指定时间（毫秒） */
    if (interval > 3600*24*30*1000){
      var days = parseInt(interval / 86400000)
      posts[0].insertAdjacentHTML('afterbegin', '<div class="note note-warning" style="font-size:0.9rem"><p>' +
      '<div class="h6">Article Timeliness Reminder</div><p>It has been ' + days + ' days since the article was published, the content may be outdated.' +
      '</p></p></div>');
    }
  })();