I did everything, checked it twice, but merge not work after those changes.
Now, posts appear one by one without merging.
Update
After couple of tests I understood that is problem in first two changes. I removed them and it works but without 10 min limit.
Addition with update date working GREAT! Thank you very much!
I changed it a little bit: added update time.
PHP Code:
$post['message'] = $doublepost['pagetext'] . "\n\n<strong><i>Added at " . vbdate($vboptions['dateformat'], TIMENOW) . ", " . vbdate($vboptions['timeformat'], TIMENOW) . "</i></strong>" . "\n" . $post['message'];