使用setTimeout表示延迟，使用click()表示触发按钮。
示例：

// ==UserScript==
// @name         Give Name Your Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Your Script Description
// @author       You
// @match        http://*/* [URL where you want to run script]
// @icon         data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==
// @grant        none
// ==/UserScript==

(function() {
  'use strict';

  var element = document.querySelector("#al_login > div.col-sm-8.container.paddingInBoxExtra.roundCornerExtra > div:nth-child(2) > input.row.btn.primary-btn.pull-right.marginBottomNone");
  if (element) {
    window.setTimeout(function() {
      element.click()
    }, 2000);

  }

})();