When you file an application via the Paris convention or directly in Japan, the time limit for filing a request for examination is three years from the filing date of the application in Japan (not three years from the priority date).  When you file a PCT application, the time limit is three years from the international filing date (not three years from the priority date, nor three years from the national entry date in Japan).  There is no system of request for examination for applications for utility model registrations in Japan.