Hi Marc!
When I click a db name on the left panel, I get 20 seconds between the "before" and "after". Can't find what is happening in header_meta_style.inc.php. There are some calls to PMA_generate_commun_url() but it does not seem to be the problem.
Are you sure it takes 20 seconds within that file, or just 20 seconds in your browser output? Because of HTTP chunking, it could appear that it takes so long for that simple file, while in real PHP time the time is spent somewhere else.
I would suggest you instead of echooing a string to echo the current timestamp, and then calculate the difference between the various timestamps...?
Regards, Garvin