I read official website's introduction, and the explanation of mutual transfer of funds is as follows:

Transfer to each other before 1)T date 15, and transfer to the new fund after confirmation on T+ 1 day.

2) The mutual transfer income is uninterrupted, and the money fund transfer income is enjoyed on T day, and the money fund transfer income is enjoyed on T+ 1 day after the confirmation is successful.

In other words, the premise is that you transfer Fund A to Fund B before the first day 15, and today you enjoy the income of Fund A; The next day (which must be a trading day), you can enjoy the income of fund B.