meeting.module

<?php

use Drupal\Core\Form\FormStateInterface;
use Drupal\node\NodeInterface;

/**
 * Implements HOOK_form_BASE_FORM_ID_alter
 * for Meeting Node forms
 * @param $form
 * @param \Drupal\Core\Form\FormStateInterface $form_state
 * @param $form_id
 */
function meeting_form_node_form_alter(&$form, FormStateInterface $form_state, $form_id) {

  switch ($form_id) {
    // Node creation form
    case "node_meeting_form":
      _setup_meeting_entity_builder($form);
      break;

    // Node edit form
    case "node_meeting_edit_form":
      _hide_immutable_fields($form);
      break;
  }

}

function _setup_meeting_entity_builder(&$form) {
  $form['title']['#access'] = FALSE;
  $form['#entity_builders'][] = 'meeting_node_builder';
}

function _hide_immutable_fields(&$form) {
// These form the title .. so it's too late to change it now!
  $form['title']['#access'] = FALSE;
  $form['field_meeting_date']['#access'] = FALSE;
  $form['field_meeting_type']['#access'] = FALSE;
}

/**
 * entity_builder for new and changed Meeting Nodes
 * @param $entity_type
 * @param NodeInterface $node
 * @param $form
 * @param FormStateInterface $form_state
 */
function meeting_node_builder($entity_type, NodeInterface $node, &$form, FormStateInterface $form_state) {
  // Construct the title from the type and date of the meeting
  $date_of_meeting = $node->field_meeting_date->date;
  $type_of_meeting_id = $form_state->getValue('field_meeting_type')[0]['target_id'];
  $referenced_tag = \Drupal::entityTypeManager()
    ->getStorage('taxonomy_term')
    ->load($type_of_meeting_id);
  $name_of_meeting = $referenced_tag->name->value;
  if ($date_of_meeting instanceof Drupal\Core\Datetime\DrupalDateTime) {
    $node->setTitle($name_of_meeting . ' on ' . $date_of_meeting->format('l, j F Y'));
  }
  else {
    $form_state->setErrorByName('field_meeting_date', "Oops! I didn't understand that date.");
  }
}