How to autofill webform with node field data
Using hook_form_alter() or hook_form_FORM_ID_alter(), you can set the default value by php code

For Example

function HOOK_form_FORM_ID_alter(&amp;$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id){
  if($form_id == 'YOUR_FROM_ID'){
    $form['submitted']['FIELDNAME']['#default_value'] = date("Y-m-d h:i a", time());
  }
}