You can consult now, because it is not easy to apply for Japan. You can prepare the deposit certificate and other materials first, and go directly to the visa after getting the diploma, which will save a lot of time. Besides, you can learn more Japanese now. You are a student of Northeastern University, that is, there are many Japanese training schools in Shenyang, and the prices are not very high. In short, you can consult the intermediary now to find out what materials are needed. If you can prepare it yourself, if you can't, let the intermediary help you. Don't wait until you graduate to apply for a visa.
The graduation process of Dongda University is unclear.