Doesn't work with Datestamp

I was checking this out. We need something similar, but group by day, not month. It didn't work until I changed

    $year  = date('Y', strtotime($val));
    $month = date('F', strtotime($val));

to
<?
$year = date('Y', $val);
$month = date('F', $val);
?>

I think you have written this module to use Date fields, and not datestamp fields, which are also available through the date field module. This could be easily checked with is_numeric($val).