how many weeks do you have on a student visa for a semester?

obviously i couldn’t detail my question out in the title.

i was wondering if there was a specific set of weeks you get before and after your first/last day of school in japan?

say, if my semester starts on october 1st and ends beginning february, can i arrive a month prior (end of august) and leave beginning march?

and before you say « contact your embassy », i will. simply, not now as my school’s still preparing all formalities.
i’d also just like to know everyone’s experiences or if there’s an objective answer to this question.

thank you!