Override of dateTime input to display datetime values in the user's timezone. Note how I include my custom class to override the Form helper class

AppController.php

<?php
App::uses('Controller', 'Controller');
App::uses('Category', 'Model');
App::uses('CakeTime', 'Utility');

/**
 * Application Controller
 *
 * @package		app.Controller
 */
class AppController extends Controller {
	
/**
 * Helpers
 * 
 * NOTE how I include the form helper here
 *
 * @var array
 */
	public $helpers = array('Session', 'Time', 'Form' => array('className' => 'Template'));

/**
 * before filter callback
 * 
 * @return void
 */
	public function beforeFilter() {
		Configure::write('Config.timezone', 'America/Jamaica');
	}
}

TemplateHelper.php

<?php
App::uses('FormHelper', 'View/Helper');
App::uses('CakeTime', 'Utility');

/**
 * Class TemplateHelper
 * 
 * NOTE It extends the form helper
 */
class TemplateHelper extends FormHelper {

/**
 * Date time input function override that allows date time inputs to display
 * the time in a user's timezone. We may need to add options to make this optional.
 *
 * @param string $fieldName
 * @param string $dateFormat
 * @param string $timeFormat
 * @param array $attributes
 * @return string
 */
	public function dateTime($fieldName, $dateFormat = 'DMY', $timeFormat = '12', $attributes = array()) {
		$attributes = parent::value($attributes, $fieldName);
		if (!empty($attributes['value'])) {
			$attributes['value'] = CakeTime::format('Y-m-d H:i:s', $attributes['value']);
		}
		return parent::dateTime($fieldName, $dateFormat, $timeFormat, $attributes);
	}
}