How long does it take after the filing of an Invalidation Trial for such fact to be available to the public?
According to the Japanese Patent Law, the fact of filing of an invalidation trial will be registered in the patent register. It should take about three weeks after the filing. After another month or so, such fact will become available on the JapanPlatPat website which is a database provided by the JPO (more precisely, JPO related organization).
The patent register is a public information. However, in order to check the patent register, one has to bother to file a request with some governmental fee and therefore, patent register is not so commonly used merely to check the status. Instead, the JapanPlatPat website is more commonly used for such purpose. As explained above, it generally takes about two months after the filing of an invalidation trial before such fact become available on the JapanPlatPat database.