Have you tried doing a whole bunch of code and it’s not working, or you’re just stumped on how you’d begin? I’m not a PHP wizard by a long shot (so I have no template to give you, sorry.) But wouldn’t it just involve using some PHP date math:
<?php
$three_days_ago = mktime(0, 0, 0, date("m") , date("d")-3, date("Y"));
?>
... and then setting ‘start_on’ to $three_days_ago? Actually you’d have to generate two PHP variables: the start date/time and the end date/time, to drop into ‘start_on’ and ‘stop_before.’
(Above code is from http://ca.php.net/date by the way)
Maybe post what you’ve got here and let us take a look at it?