hook_form_alter(&$form, &$form_state, $form_id) {

    // http://drupal.org/node/1455576 - Date
    $form['field_date'][LANGUAGE_NONE][0]['value'] = time();

    // http://drupal.org/node/1455576 - Date (ISO Format)
    $form['field_date_iso_format'][LANGUAGE_NONE][0]['value'] = time();

    // http://drupal.org/node/1455576 - Date (Unix Timestamp)
    $form['field_date_unix_timestamp'][LANGUAGE_NONE][0]['value'] =time();
}

$node->field_date[LANGUAGE_NONE][0] = array(
    'value' => format_date(strtotime('now'), 'custom', 'Y-m-d H:i:s', 'UTC'),
    'timezone' => 'UTC',
    'timezone_db' => 'UTC',
  );

// For datetime
$node->field_datetest[$node->language][0]['value'] = "2011-05-25 10:35:58";

// For date
$node->field_datetest[$node->language][0]['value'] = "2011-05-25T10:35:58";

// For datestamp
$node->field_datetest[$node->language][0]['value'] = strtotime("2011-05-25 10:35:58");

$node->field_date[LANGUAGE_NONE][0] = array(
      'value' => date('Y-m-d H:i:s', strtotime('now')),
      'timezone' => 'UTC',
      'timezone_db' => 'UTC',
);

jQuery(document).ready(function() {

    var fullDate = new Date()
    var HR_fullDate = fullDate.toDateString().toString().substring(4,15);
    jQuery('strong.date').contents().replaceWith(HR_fullDate);

});

$mydate = date('Y-m-d', strtotime('31 May 2011'));

$node->field_datetest[$node->language][0][value] = "2011-05-25T10:35";

$now = date_now('UTC');
$now = date_format($now, "Y-m-d H:i:s");

// The date format in this sample is dd/mm/yyyy
$form_state['values']['field_my_date_field']['und'][0]['value']['date'] = '14/05/2014';

function MY_MODULE_node_presave($node)
  {
      $node->field_date['und'][0]['value'] =  '2014-09-23 00:00:00';
  }

function MY_MODULE_node_submit($node, $form, &$form_state) {
  if($node->type == 'my_node_type') {
    $test_date =  $form['test_date ']['#value'];
    //Ensure that $test_date format is '2014-09-23 00:00:00'
    $node->field_date['und'][0]['value'] =  $test_date ;
   }
}

$entity->field_upload_time["und"][0]["value"] = time();