How can I add a delay to the collapsible menu in Twenty Eleven?

Superfish is a script that will add a delay to the hover action. It is used in a lot of themes, for instance I know it is used in the Thematic Theme. Untested, but I think this is how you’d apply it (based on the docs).

function wp88740_enqueue(){
  wp_enqueue_script('jquery');
  wp_enqueue_script('hoverintent', get_stylesheet_directory() . '/scripts/hoverIntent.js' );
  wp_enqueue_script('superfish', get_stylesheet_directory() . '/scripts/superfish.js' );
}
add_action('wp_enqueue_scripts','wp88740_enqueue');

function wp88740_initialize(){ ?>

// initialise Superfish
<script>

    jQuery(document).ready(function($){
        $("#access ul.menu").superfish();
    });

</script>
<?php }
add_action('wp_head','wp88740_initialize');