Delay for Simple HTML DOM Class
PHP runs on the server. JavaScript (e.g. AJAX) runs in the browser, after the PHP code on the server has finished producing the page. You can't make a PHP program, running on the server, wait for an event that happens later in the browser.
You'll need to either load the content for that div using PHP code, or replace the PHP DOM-parsing code with JavaScript code that does the work on the client.