Thanks Lothor!
Hi RISTIK, I don't know how long it takes but I can maybe give you a reasonable estimate for Canada. The application for graduate studies was due on the 18th of May, I applied in the Toronto Japanese Embassy. On the embassy website it says the exam/interview will take place late June or early July and we haven't gotten an email yet. The undergraduate applications were due today (June 2nd) so I'm assuming the embassy is going to contact both undergraduate applicants and post-graduate applicants once both have been screened. I would expect to get an email some time next week because there aren't many applicants from Canada so not much time for document screening is needed. (Also confirmed with my embassy, they will contact everyone, not just the people who pass the document screening).
TL;DR: I don't know the exact time frame, but for Canada it is going to be anywhere from 20 to 30 days (even though Canada doesn't have many applicants for post-graduate, according to my embassy) from deadline of application to recieving email of invitation to exam/interview or rejection.
Anyway, I will update this forum with the exact dates of when I get the email ragardless of acceptance or rejection.