Unfortunately it’s not possible to schedule your tags to play directly. However, there is another way to obtain the same result:
1) Create an automatic playlist in your music library
2) Click on add a criterion
3) Choose Tag > CONTAINS or EQUAL TO > enter the name of your tag
4) Don't forget to give your playlist a name before saving
Once that’s done, you can add your playlist to your Planning. Your playlist will automatically update itself when you add or remove MP3 files to your tag.
Careful: when you schedule your playlist in the Planning Tab, make sure to regenerate your day under the Daily Generation Tab so that your changes are taken into account.