Place the following in your functions.php file for the active theme:

function edit_link_update($link_ID) {

	global $wpdb;

	$sql = "update wp_links set link_updated = NOW() where link_id = " . $link_ID . ";";

	$wpdb->query($sql);

}

add_action('edit_link', 'edit_link_update');



function get_bookmarks_fresh($args, $days_old = 30) {

	$bookmarks = get_bookmarks($args);

	$str = '';

	foreach ($bookmarks as $b) {

		$datediff = ((((date('U') - date('U', strtotime($b->link_updated))) / 60) / 60) / 24);

		$str .= '<li><a' . ($datediff <= $days_old ? ' class="new"' : '') . ' href="' . $b->link_url . '" title="' . $b->link_description . '">' . $b->link_name . '</a></li>';

	}

	echo $str;

}

Then where you would normally put "wp_list_bookmarks", put "get_bookmarks_fresh" instead, like:

get_bookmarks_fresh('orderby=name');

I have found that "link_updated" doesn't seem to be set correctly in a default WP install, which is why the 'edit_link_update' function is there.

Also, I should mention that editing core file like "/wp-includes/bookmark-template.php" is not such a great plan, as an upgrade may destroy your changes.