Here is something I just banged out. It's really just a nice human interface for adding seconds to the passed timestamp, but it works.
BTW: There are only 78 shopping weeks until Christmas 2005.
<?php
function add_to_time($number,$span,$start = '') {
$start = intval($start);
$number = intval($number);
$valid_spans = array('week' => 604800,'day' => 86400,'hour' => 3600,'minute' => 60,'second' => 1);
if($start == 0) {$start = time();}
if($number < 1) {return 0;}
if(!in_array($span,array_keys($valid_spans))) {return 0;}
$offset = $number * $valid_spans[$span];
return ($start + $offset);
} //end in_milti_dim_array
?>