How to alter the fields available for commerce backoffice Quick Edit? I have added a "waiting time" field to the orders in Drupal Commerce, so that each order has a waiting time. 

I would like for the field to be available using the Quick Edit options of Commerce Backoffice. How to do it?
i am not sure if this might help, but recently i've written a custom hook to enable stock quantity field on commerce product quick edit form.

It should theoretically be possible yes to write a similar hook on commerce order.
Here's my custom module copy pasted : 

&lt;?php
/**
 * Implements hook_form_FORM_ID_alter().
 */
function commerce_stock_quickedit_form_commerce_backoffice_product_quick_edit_form_alter(&amp;$form, &amp;$form_state, &amp;$product){
  $product = $form_state['product'];
  $product_wrapper = entity_metadata_wrapper('commerce_product', $product);
  $form['stock'] = array(
    '#type' =&gt; 'textfield',
    '#title' =&gt; t('Stock'),
    '#title_display' =&gt; 'before',
    '#default_value' =&gt; !empty($product-&gt;commerce_stock) ? $product_wrapper-&gt;commerce_stock-&gt;value() : 0,
    '#size' =&gt; 5,
  );
  $form['price']['#title_display'] = 'before';
  $form['#validate'][] = 'commerce_stock_quickedit_commerce_backoffice_product_quick_edit_form_validate';
  $form['#submit'][] = 'commerce_stock_quickedit_commerce_backoffice_product_quick_edit_form_submit';
}
/**
 * Validation callback to make sure stock is numeric.
 */
function commerce_stock_quickedit_commerce_backoffice_product_quick_edit_form_validate($form, &amp;$form_state) {
  if (!empty($form_state['values']['stock'])) {
    if (!is_numeric($form_state['values']['stock'])) {
      form_set_error('stock', t('Please enter a numeric stock value'));
    }
  }
}
/**
 * Submit callback to update the product stock.
 */
function commerce_stock_quickedit_commerce_backoffice_product_quick_edit_form_submit($form, $form_state) {
  $product = $form_state['product'];
  if (!empty($product) &amp;&amp; !empty($form_state['values']['stock'])) {
    $product_wrapper = entity_metadata_wrapper('commerce_product', $product);
    $product_wrapper-&gt;commerce_stock-&gt;set($form_state['values']['stock']);
    commerce_product_save($product);
  }
}