Wow, that's a crazy date format, probably easiest to use a regular expression to isolate each part and then call strtotime() on the result.
Perhaps something like:
<?php
$date = '24Oct3PM';
preg_match('/^([0-9]{1,2})([a-z]{3})([0-9]{1,2})([APM]{2})$/i', $date, $matches);
list(,$day,$month,$time,$meridiem) = $matches;
$unix_time = strtotime("$month $day 2008 $time $meridiem");
?>