function sec_to_time($seconds) {
    $units = array(
        array('day', 60*60*24),
        array('hour', 60*60),
        array('minute', 60),
        array('second', 1)
    );
    $modf_ = array();
    foreach ($units as $u) {
        list($descr, $div) = $u;
        $n = floor($seconds / $div);
        if ($n || (!$modf_ && 1 == $div))
            $modf_[] = sprintf('%d %s%s', $n, $descr, $n == 1 ? '' : 's');
        $seconds -= $n * $div;
    }
    return join(', ', $modf_);
}