Magento 1.9 – Admin Form Save Date Format Issue

I'm not sure if this is the best solution, but I think it should work:

Add a custom renderer to the textfield that will format the date:

$renderer = $this->getLayout()->createBlock('foo/widget_grid_renderer_date');
$fieldset->addField('end_date', 'text', array(
            'label'     => Mage::helper('survey')->__('End Date'),
            'index'     => 'end_date',
            'name'      => 'end_date',
            'class'     => 'readonly',
            'readonly'  => true
      )
    )->setRenderer($renderer);

Create a new renderer class:

class Example_Foo_Block_Widget_Grid_Renderer_Date extends Mage_Adminhtml_Block_Template 
    implements Varien_Data_Form_Element_Renderer_Interface
{

    public function render() {

        //...
        return Mage::getSingleton('core/locale')
                        ->date($data, Zend_Date::ISO_8601, null, false)->toString($format);     
    }
}

For correct date's output use date_format property

  $fieldset->addField(
         'birthdate',
         'date',
         [
             'name' => 'birthdate',
             'label' => __('Birthdate'),
             'title' => __('Birthdate'),
             'required' => true,
             'class' => '',
             'singleClick'=> true,
             'date_format' => 'yyyy-MM-dd', **//Like this one**
             'time'=>false
            //'format' =>$this->_localeDate->getDateFormat(\IntlDateFormatter::LONG)
         ]
     );