<?php

/**
 * Implements hook_form_alter().
 */

function date_selection_display_form_alter(&$form, \Drupal\Core\Form\FormStateInterface &$form_state, $form_id) {
  $form['field_date']['#states'] = [
    'visible' => [
      ':input[name="field_date_checkbox"]' => ['checked' => 'TRUE']
    ]
  ];
  $form['field_date_time']['#states'] = [
    'visible' => [
      ':input[name="field_date_checkbox"]' => ['checked' => 'FALSE']
    ]
  ];
}