rangos de tiempos

 def valid_start_work_time?
    return false unless valid_work_time? && valid_spare_time?

    errors.add(:spare_time, 'error generico numero 1') if work_time.first >= spare_time.first
    return true
  end

  def valid_end_work_time?
    return false unless valid_work_time? && valid_spare_time?

    errors.add(:spare_time, 'error generico numero 2') if work_time.last <= spare_time.last
    return true
  end