diff --git a/core/modules/datetime/datetime.module b/core/modules/datetime/datetime.module
index f68bf7e..823de33 100644
--- a/core/modules/datetime/datetime.module
+++ b/core/modules/datetime/datetime.module
@@ -10,7 +10,7 @@
 /**
  * Defines the timezone that dates should be stored in.
  *
- * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x. Use
+ * @deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use
  * \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::STORAGE_TIMEZONE
  * instead.
  */
@@ -19,7 +19,7 @@
 /**
  * Defines the format that date and time should be stored in.
  *
- * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x. Use
+ * @deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use
  * \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATETIME_STORAGE_FORMAT
  * instead.
  */
@@ -28,7 +28,7 @@
 /**
  * Defines the format that dates should be stored in.
  *
- * @deprecated in Drupal 8.3.x and will be removed before Drupal 9.0.x. Use
+ * @deprecated in Drupal 8.5.x and will be removed before Drupal 9.0.x. Use
  * \Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface::DATE_STORAGE_FORMAT
  * instead.
  */
diff --git a/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php
index a027a82..4b2ad5d 100644
--- a/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php
+++ b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php
@@ -4,6 +4,7 @@
 
 use Drupal\Component\Datetime\DateTimePlus;
 use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
 
@@ -24,10 +25,10 @@ public function validate($item, Constraint $constraint) {
       }
       else {
         $datetime_type = $item->getFieldDefinition()->getSetting('datetime_type');
-        $format = $datetime_type === DateTimeItem::DATETIME_TYPE_DATE ? DATETIME_DATE_STORAGE_FORMAT : DATETIME_DATETIME_STORAGE_FORMAT;
+        $format = $datetime_type === DateTimeItem::DATETIME_TYPE_DATE ? DateTimeItemInterface::DATE_STORAGE_FORMAT : DateTimeItemInterface::DATETIME_STORAGE_FORMAT;
         $date = NULL;
         try {
-          $date = DateTimePlus::createFromFormat($format, $value, new \DateTimeZone(DATETIME_STORAGE_TIMEZONE));
+          $date = DateTimePlus::createFromFormat($format, $value, new \DateTimeZone(DateTimeItemInterface::STORAGE_TIMEZONE));
         }
         catch (\InvalidArgumentException $e) {
           $this->context->addViolation($constraint->badFormat, [
diff --git a/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php b/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
index 9884007..fbcedbd 100644
--- a/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
+++ b/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
@@ -5,6 +5,7 @@
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FieldItemInterface;
 use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItemInterface;
 use Drupal\entity_test\Entity\EntityTest;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\Tests\field\Kernel\FieldKernelTestBase;
@@ -80,19 +81,19 @@ public function testDateTime() {
     $this->assertTrue($entity->field_datetime[0] instanceof FieldItemInterface, 'Field item implements interface.');
     $this->assertEqual($entity->field_datetime->value, $value);
     $this->assertEqual($entity->field_datetime[0]->value, $value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Verify changing the date value.
     $new_value = '2016-11-04T00:21:00';
     $entity->field_datetime->value = $new_value;
     $this->assertEqual($entity->field_datetime->value, $new_value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Read changed entity and assert changed values.
     $this->entityValidateAndSave($entity);
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime->value, $new_value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test the generateSampleValue() method.
     $entity = EntityTest::create();
@@ -121,19 +122,19 @@ public function testDateOnly() {
     $this->assertTrue($entity->field_datetime[0] instanceof FieldItemInterface, 'Field item implements interface.');
     $this->assertEqual($entity->field_datetime->value, $value);
     $this->assertEqual($entity->field_datetime[0]->value, $value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Verify changing the date value.
     $new_value = '2016-11-04';
     $entity->field_datetime->value = $new_value;
     $this->assertEqual($entity->field_datetime->value, $new_value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Read changed entity and assert changed values.
     $this->entityValidateAndSave($entity);
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime->value, $new_value);
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test the generateSampleValue() method.
     $entity = EntityTest::create();
@@ -158,7 +159,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with string value.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test DateTimeItem::setValue() using property array.
     $entity = EntityTest::create();
@@ -169,7 +170,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with array value.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test a date-only field.
     $this->fieldStorage->setSetting('datetime_type', DateTimeItem::DATETIME_TYPE_DATE);
@@ -184,7 +185,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with string value.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test DateTimeItem::setValue() using property array.
     $entity = EntityTest::create();
@@ -195,7 +196,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with array value.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
   }
 
   /**
@@ -215,7 +216,7 @@ public function testSetValueProperty() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, '"Value" property can be set directly.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test Date::setValue() with a date-only field.
     // Test a date+time field.
@@ -230,7 +231,7 @@ public function testSetValueProperty() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, '"Value" property can be set directly.');
-    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+    $this->assertEquals(DateTimeItemInterface::STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
   }
 
   /**