Rich Snippets Error Missing required field "updated"

I am using a theme based on Twenty Eleven Version: 1.4
It fails the Google Rich Snippets testing tool on only one point – Warning: Missing required field “updated”.

I think the problem is in

function twentyeleven_posted_on() {
	printf( __( '<span class="sep">Posted on </span><a href="%1$s" title="%2$s" rel="bookmark"><time class="entry-date" datetime="%3$s" pubdate>%4$s</time></a><span class="by-author"> <span class="sep"> by </span> <span class="author vcard"><a class="url fn n" href="%5$s" title="%6$s" rel="author">%7$s</a></span></span>', 'twentyeleven' ),
		esc_url( get_permalink() ),
		esc_attr( get_the_time() ),
		esc_attr( get_the_date( 'c' ) ),
		esc_html( get_the_date() ),
		esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ),
		esc_attr( sprintf( __( 'View all posts by %s', 'twentyeleven' ), get_the_author() ) ),
		get_the_author()
	);

My tentative solution is to change time class="entry-date" to time class="updated" but I am not sure if doing this would badly effect anything else – was it named entry-date for a reason that I am ignorant of?

Replies and comments would be much appreciated.