Tourism before school

Hello! I will be attending Sapporo University as an exchange student this fall! I know that I, on a student visa, am not eligible for a rail pass, but I'm planning to come into the country a couple weeks before school will start to travel around a little.

So my question, I suppose, is this: if I come into the country the last week of August and school doesn't start until September 20, am I eligible for a jr pass during the time that I am NOT in school?