Getting an element of a CCK field to use and modify in hook_form after_build
You are on the right track. You want to set the #title attribute of the form element whose label you want to change, which can all be done at the hook_form_alter() time.

In order to change the label of the 'week_night' form element, try something like this:

function rates_override_form_alter(&amp;$form, $form_state, $form_id) {
  if($form_id == 'ldisilink_property_node_form') {
    $form['field_rates']['week_night']['#title'] = t('My new label');
}


This is assuming the 'week_night' form element is nested within 'field_rates' fieldset. If that is not the case, use:

$form['week_night']['#title'] = t('My new label');


instead.