So, I guess I was lucky ?
When I started looking into changing status of residence a couple weeks ago, read many things online that it’ll be hard to do it while on a tourist visa.
Decided to call the Immigration Office (went with Tachikawa, as I wanted to avoid Shinagawa) and they told me that I would probably be fine.
Went to apply beginning of April (3 days before my tourist visa expired), they gave me a two month extension and after two weeks I received a letter asking for additional documents, which I sent. After a week I received the postcard and went today to the immigration office.
Took ~ 4 weeks in total.
by iLouiis