Timestamp problem

I use PHP 4.4.0 and MySQL 4.0.26 and Mozilla Firefox.

This code:

$dummy = strtotime("-13 hour");
$csql = "update citc_weather
        set imagepath = '$p_image',
        text = '$p_text',
        lastupdated = $dummy
        where id = 1";

where lastupdated is of timestamp(14), doesn't work.

All that gets posted in lastupdated is 00000000000000.
Received on Tue Oct 18 02:31:05 2005