<?php

namespace Opifer\EavBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
* DateTimeValue
*
* @ORM\Entity
*/
class DateTimeValue extends Value
{
    /**
    * Turn value into string for form field value purposes
    *
    * @return string
    */
    public function __toString()
    {
        return (string) $this->getTimestamp();
    }

    /**
     * Get value
     *
     * @return \DateTime
     */
    public function getValue()
    {
        $datetime = new \DateTime();

        return $datetime->setTimestamp($this->value);
    }

    /**
     * Set value
     *
     * @param \DateTime $value
     *
     * @return DateTimeValue
     */
    public function setValue($value)
    {
        $this->value = $value->getTimestamp();

        return $this;
    }

    /**
     * Get raw value
     *
     * @return string
     */
    public function getTimestamp()
    {
        return $this->value;
    }
}

<?php

namespace Opifer\EavBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
* DateTimeValue
*
* @ORM\Entity
*/
class DateTimeValue extends Value
{
    /**
    * Turn value into string for form field value purposes
    *
    * @return string
    */
    public function __toString()
    {
        return date('d-m-Y H:i:s', $this->getTimestamp());
    }

    /**
     * Get value
     *
     * @return \DateTime
     */
    public function getValue()
    {
        $datetime = new \DateTime();

        return $datetime->setTimestamp($this->value);
    }

    /**
     * Set value
     *
     * @param \DateTime $value
     *
     * @return DateTimeValue
     */
    public function setValue($value)
    {
        $this->value = $value->getTimestamp();

        return $this;
    }

    /**
     * Get raw value
     *
     * @return string
     */
    public function getTimestamp()
    {
        return $this->value;
    }
}

Return readable date format in toString
Return readable date format in toString