Hawzah News Agency – With regard to a recommended fast or an obligatory fast that does not have an assigned time – such as a fast for kaffārah – if someone decides to do something that invalidates a fast or is indecisive as to whether or not to invalidate it, then, in the event that he does not do so and makes the intention to fast again before ẓuhr in the case of an obligatory fast, and before sunset (ghurūb) in the case of a recommended fast, his fast is valid.

Source: https://www.sistani.org/english/book/48/