Couldn't he just put the following straight into the page?
Code:
<?PHP
//Current hour of day, this is in the server time
$CurHour = date('H');
//If it's greater than or equal to 22 i.e. 10 or 11PM
//Or if it's less than or equal 08 i.e. 00,01,...,08AM
//Include the banner.htm otherwise do nothing
if ($CurHour>=22 || $CurHour<8) {
print 'HTML CODE FOR THE BANNER GOES HERE';
}
?>
remembering of course that he has to change the extension of the page this code is used on to .php so that the server knows to send it to the PHP processor first.