Seems that after setting the session id, a flush isnt working.
If you supply a PHPSESSID, then it doesnt output anything until the end of the script, without the PHPSESSID, then it does what you would expect, output one stamp, then another after 10 seconds.

<?
  if ( $_GET["PHPSESSID"] ) {
    $PHPSESSID = $_GET["PHPSESSID"];  
    session_id($PHPSESSID);  
  }
  session_start();
  for($i=0; $i<300; $i++ ) {
    echo "\n";
  }
  
  echo gmdate("H:i:s");
  echo "<BR>";
  flush();  
  sleep(10);
  echo gmdate("H:i:s");
  echo "<BR>";
?>

'./configure' 
'--with-apxs=/usr/local/apache-1.3.26/bin/apxs' 
'--with-mysql' 
'--with-mhash' 
'--enable-track-vars=yes' 
'--enable-debug=no' 
'--enable-force-cgi-redirect=yes' 
'--enable-calendar' 
'--with-gd=/export/home/hostel/Installs/gd-1.8.4' 
'--with-png-dir=/export/home/hostel/Installs/libpng-1.0.12' 
'--with-zlib' 
'--with-jpeg-dir=/export/home/hostel/Installs/jpeg-6b' 
'--enable-mbstring' 
'--enable-mbstr-enc-trans' 
'--enable-trans-sid'