1.form.php

        $hydra = new DoctrineHydrator($sm->get('Doctrine\ORM\EntityManager', false));
        $hydra->addStrategy('date_start', new \cwdCommon\Doctrine\Strategy\DateTime());
        $hydra->addStrategy('date_end', new \cwdCommon\Doctrine\Strategy\DateTime());

        $this->setHydrator($hydra);
        $this->setObject(new \Application\Entity\Event());

        $this->add(
            array(
                'name'  => 'date_start',
                'options' => array(
                    'label' => 'Date'
                ),
                'attributes' => array(
                    'id' => 'date-from-raw'
                )
            )
        );

        $this->add(
            array(
                'name'  => 'date_end',
                'options' => array(
                    'label' => 'Date'
                ),
                'attributes' => array(
                    'id' => 'date-to-raw'
                )
            )
        );

2.DateTime.php

<?php

namespace cwdCommon\Doctrine\Strategy;

use Zend\Stdlib\Hydrator\Strategy\StrategyInterface;

class DateTime implements StrategyInterface
{
    /**
     * Converts the given value so that it can be extracted by the hydrator.
     *
     * @param mixed $value The original value.
     * @return mixed Returns the value that should be extracted.
     */
    public function extract($value)
    {
        return 'extract';
    }

    /**
     * Converts the given value so that it can be hydrated by the hydrator.
     *
     * @param mixed $value The original value.
     * @return mixed Returns the value that should be hydrated.
     */
    public function hydrate($value)
    {
        return 'hydrate';
    }

}