Additional text code at the end of post content appears at the blog page, too

Hi,

I’m using the “elegant blog layout” and added in loop-index.php this code snippet; it shows, when a post has been updated:

if(strtotime($post->post_modified) - strtotime($post->post_date) > 86400) {  
echo "<span class='aktualisiert'>(aktualisiert: ",
the_modified_date('j. M. Y').')</span></span>';
}

It should appear only at the bottom of a single post – so far, so good, it works: http://screencloud.net/v/juON

I have added this code snippet in the loop-index.php at line 207-209:
http://pastebin.com/5xnZ6zku

The problem is:
it shows this “updated time” also at the blog page below the excerpt and the “read more” button:
http://screencloud.net/v/jSNs

Could you please tell me, where exactly in the loop-index.php I can place the code snippet mentioned above,
so that it appears only in single post, but not at the blog page under each post preview/excerpt?

Thank you.