Drupal db_select with BETWEEN not working

I am trying to build a list of nodes that have a publication date between two days ago and now.  I tried this:

  $query = db_select('node', 'n');
  $query->join('field_data_field_pubdate', 'f', 'n.nid = f.entity_id'); //JOIN node with pubdate
  $query->fields('n', array('nid', 'created', 'title'));
  $query->addField('f', 'field_pubdate_value', 'pubdate');
  $query->condition('n.type', variable_get('ain_sitemap_node_types', array_keys(node_type_get_names())));
  $query->condition('n.status', NODE_PUBLISHED);
  $query->condition('f.field_pubdate_value', array(REQUEST_TIME - 172800, REQUEST_TIME), 'BETWEEN');
  $query->addTag('node_access'); 
  $query->orderBy('f.field_pubdate_value', 'DESC'); 
  $query->range(0, 1000); 
  $nodes = $query->execute()->fetchAll(); 

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But it's not working - now, it's just the one row with the BETWEEN clause (Line 7) - if I replace with this:

$query->condition('f.field_pubdate_value', REQUEST_TIME - 172800, '>=');

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It works fine.  But this returns nodes with a pubdate value greater than right now, which I don't want.