--- src/Plugin/Field/FieldWidget/TimestampDatetimeNoDefaultWidget.5	2016-02-01 08:46:53.000000000 +0000
+++ src/Plugin/Field/FieldWidget/TimestampDatetimeNoDefaultWidget.php	2016-02-01 08:53:21.000000000 +0000
@@ -18,8 +18,8 @@
  *
  * @FieldWidget(
  *   id = "datetime_timestamp_no_default",
- *   label = @Translation("Datetime Timestamp no default"),
- *   description = @Translation("An optional datetime field. Does not provide a default time if left blank."),
+ *   label = @Translation("Datetime Timestamp with no default"),
+ *   description = @Translation("An optional datetime field. Does not provide a default time if left blank. Defined by Scheduler module."),
  *   field_types = {
  *     "timestamp",
  *   }
@@ -32,11 +32,13 @@
    */
   public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
     $element = parent::formElement($items, $delta, $element, $form, $form_state);
-    // @todo Do not these lines. The #description is entirely replaced by custom
-    // text in scheduler_form_node_form_alter()
+    // Remove 'Leave blank to use the time of form submission' which is in the
+    // #description inherited from TimestampDatetimeWidget. The text here is not
+    // used because it is entirely replaced in scheduler_form_node_form_alter()
+    // However the widget is generic and may be used elsewhere in future.
     $date_format = DateFormat::load('html_date')->getPattern();
     $time_format = DateFormat::load('html_time')->getPattern();
-    $element['value']['#description'] = $this->t('Format: %format. Leave blank to disable.', array('%format' => Datetime::formatExample($date_format . ' ' . $time_format)));
+    $element['value']['#description'] = $this->t('Format: %format. Leave blank for no date.', array('%format' => Datetime::formatExample($date_format . ' ' . $time_format)));
 
     // Set the callback function to allow interception of the submitted user
     // input and add the default time if needed. It is too late to try this in
@@ -50,10 +52,10 @@
    *
    * This will intercept the user input before form validation is processed.
    */
-  public function valueCallback(&$element, $input, FormStateInterface $form_state) {
+  public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
     if ($input !== FALSE) {
-      $date_input  = $element['#date_date_element'] != 'none' && !empty($input['date']) ? $input['date'] : '';
-      $time_input  = $element['#date_time_element'] != 'none' && !empty($input['time']) ? $input['time'] : '';
+      $date_input = $element['#date_date_element'] != 'none' && !empty($input['date']) ? $input['date'] : '';
+      $time_input = $element['#date_time_element'] != 'none' && !empty($input['time']) ? $input['time'] : '';
       // If there is an input date but no time and the date-only option is on
       // then set the input time to the default specified by scheduler options.
       $config = \Drupal::config('scheduler.settings');