Japan cold have a nuclear bomb ready to be dropped within 60 days. It already has the fissile material and the empty internal matrix for many such devices, IMHO.If it did not, it would be a startegic idiocy.Japan is a master of strategy in foreign affairs and in war.
I doubt if it would take that long. While I’m sure Japan doesn’t now have one, I’m also sure that they’ve got a “just in time” assembly process set up somewhere and have run all the computer models they need. The only thing I’m unsure about is the amount of weapons-grade material they have squirreled away.