MySQL's UNIX_TIMESTAMP should do the trick:
$begin_range = mktime(0, 0, 0, 6, 10, 2004);
$end_range = mktime(0, 0, 0, 6, 12, 2004);
$sql = "SELECT UNIX_TIMESTAMP(ClickTime)
FROM table
WHERE (UNIX_TIMESTAMP(ClickTime) > $begin_range)
AND (UNIX_TIMESTAMP(ClickTime) < $end_range)";
Hope that helped.