This worked for me to get and set the date field value using presave hook based on content type
/**
 * Implements hook_entity_presave().
 */

function YOUR_MODULE_global_entity_presave(Drupal\Core\Entity\EntityInterface $entity) 
{
  if ($entity->bundle() == 'blog') {
    $published = $entity->get('created')->value;
    $entity->set('field_published_date', date('Y-m-d\TH:i:s', $published));
 }
}