diff --git a/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php b/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
index 1ffa010916..54032776ef 100644
--- a/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
+++ b/core/lib/Drupal/Core/Datetime/Plugin/Field/FieldWidget/TimestampDatetimeWidget.php
@@ -29,13 +29,15 @@ class TimestampDatetimeWidget extends WidgetBase {
   public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
     $date_format = DateFormat::load('html_date')->getPattern();
     $time_format = DateFormat::load('html_time')->getPattern();
-    $default_value = isset($items[$delta]->value) ? DrupalDateTime::createFromTimestamp($items[$delta]->value) : '';
+
+    $parent_entity = $items->getParent()->getValue();
+    $default_value = (!$parent_entity->isNew() && isset($items[$delta]->value)) ? DrupalDateTime::createFromTimestamp($items[$delta]->value) : '';
     $element['value'] = $element + [
       '#type' => 'datetime',
       '#default_value' => $default_value,
       '#date_year_range' => '1902:2037',
     ];
-    $element['value']['#description'] = $this->t('Format: %format. Leave blank to use the time of form submission.', ['%format' => Datetime::formatExample($date_format . ' ' . $time_format)]);
+    $element['value']['#description'] = $this->t('Leave blank to use the time of form submission.');
 
     return $element;
   }