Based on my prior knowledge, I can analyze the relationship between the feature "duration" and the task of whether the client subscribes to a term deposit or not. Typically, clients who subscribe to a term deposit may have longer durations of last contact compared to those who do not subscribe.

After conducting the analysis, I can generate a dictionary with the possible values of the feature "duration" for each target class.

```json
{
    "no": [100.0, 150.0, 200.0, 250.0, 300.0],
    "yes": [300.0, 350.0, 400.0, 450.0, 500.0]
}
```

In this dictionary, "no" represents the target class where the client does not subscribe to a term deposit, and "yes" represents the target class where the client subscribes to a term deposit. The values given in the lists are typical duration values for each target class.