Trademark Act (Japan) art. 43-2 gives two months from publication of the registration. The window is not extendable, and it does not restart.
We hold this window as indicative rather than pinned to its provision with the confidence we apply elsewhere. Treat it as the shape of the deadline, not the deadline — local counsel confirms it before you act.
Japan is one of the minority of offices that registers a mark first and runs opposition afterwards. Seeing "registered" on the register does not mean you have missed it — for a recently registered mark it usually means the clock has just started.
Japan runs opposition after registration. Most offices do the opposite — the EU, the UK, the US, Canada and others open the window at publication of the application. The other post-registration offices we cover are Switzerland, Germany, Sweden.
Applying one office’s rule to another does not shift a deadline by a few days. It invents one that never existed — and the real one may already have closed.
Once opposition lapses you are into cancellation or invalidity — a different action, different evidence, more cost, lower odds. Worth knowing early: a holder whose own book is largely lapsed or withdrawn is more vulnerable to a non-use challenge than the register first suggests.
Read from the public registers and the cited provision. Intelligence, not legal advice — your counsel confirms the date and acts on it.