The best contact period with the professor is six months before the beginning of the wish period. At this time, the professor basically knows how many students he wants and is willing to consider this upcoming thing. Of course, in most cases, it comes first and then comes. Even so, try to get in touch (at least try to score in the language exam) on the premise that you have enough chips. In order to avoid failure.

The latest time to contact the professor when applying for Japanese graduate students:

You can still contact the professor as long as the deadline for making a wish hasn't arrived. However, it takes at least 1-2 weeks to prepare materials and mail them, so the latest deadline for contacting professors is 1-2 weeks of the deadline for making wishes.

Generally speaking, students who entered the school in April, the time is from June 10 to June 10, and June10, and the time is from April to May of that year. However, the time for students to leave voluntarily and enter the university may be different. I hope the students will investigate in advance and don't miss the time.