$result = Doctrine_Query::create()
          ->from('Day d')
          ->where('d.date BETWEEN ? AND ?', array($beginDate, $endDate))
          ->getDql();
var_dump($result);

Output: string ' FROM Day d WHERE d.date BETWEEN ? AND ?' (length=40)

-------------------------------------------------------------------------

$result = Doctrine_Query::create()
          ->from('Day d')
          ->where('d.date BETWEEN ? AND ?', array($beginDate, $endDate))
          ->getSql();
var_dump($result);

Ouput:
string 'SELECT t.id AS t__id, t.date AS t__date, t.begintime AS t__begintime, t.endtime AS t__endtime, t.workingtime AS t__workingtime, t.comment AS t__comment, t.user_id AS t__user_id FROM test_arbeitszeitkonto_days t WHERE (t.date BETWEEN ? AND )' (length=240)

==> The second question mark is missing in the SQL output and the resulting query.