Index: wp-admin/edit-form-advanced.php
===================================================================
--- wp-admin/edit-form-advanced.php	(revision 6755)
+++ wp-admin/edit-form-advanced.php	(working copy)
@@ -133,8 +133,11 @@
 	$time = __('Published on:<br />%1$s at %2$s');
 else
 	$time = __('Saved on:<br />%1$s at %2$s');
+	
+$date = ($post->post_date != '0000-00-00 00:00:00') ? $post->post_date : $post->post_modified;
+
 ?>
-<p><?php printf($time, mysql2date(get_option('date_format'), $post->post_date), mysql2date(get_option('time_format'), $post->post_date)); ?>
+<p><?php printf($time, mysql2date(get_option('date_format'), $date), mysql2date(get_option('time_format'), $date)); ?>
 <?php endif; ?>
 </div>
 
Index: wp-admin/edit-page-form.php
===================================================================
--- wp-admin/edit-page-form.php	(revision 6755)
+++ wp-admin/edit-page-form.php	(working copy)
@@ -98,8 +98,11 @@
 	$time = __('Published on:<br />%1$s at %2$s');
 else
 	$time = __('Saved on:<br />%1$s at %2$s');
+
+$date = ($post->post_date != '0000-00-00 00:00:00') ? $post->post_date : $post->post_modified;
+
 ?>
-<p><?php printf($time, mysql2date(get_option('date_format'), $post->post_date), mysql2date(get_option('time_format'), $post->post_date)); ?>
+<p><?php printf($time, mysql2date(get_option('date_format'), $date), mysql2date(get_option('time_format'), $date)); ?>
 <?php endif; ?>
 </div>