1//load external js file into header after 2 seconds
2setTimeout(function() {
3    var headerEl = document.getElementsByTagName("head")[0];   
4    var scriptEl = document.createElement('script');
5	    scriptEl.type = 'text/javascript';
6    	scriptEl.src = 'http:/www.mywebsite.com/myscript.js';
7    	headerEl.appendChild(scriptEl);
8}, 2000);