$query = $this->db->get();
    $result =  $query->result_array();


    $options = '';
    $options .= '<option selected disabled>Selecione o Horário</option>';

    foreach ($result as $key => $value)  {
        $options  .= '<option value="'.$value['id_horas'].'">'. $value['horas'].'</option>';
    }
    echo $options;