code: func durationHook(from, to reflect.Type, data reflect.Value) (reflect.Value, error) {
  	if from.Kind() != reflect.String || to != _typeOfDuration {
  		return data, nil
  	}
  
  	d, err := time.ParseDuration(data.String())
  	return reflect.ValueOf(d), err
  }
docs: // A DecodeHookFunc which decodes strings into time.Durations.