When Japan would recognize a larger County-class threat

How quickly would Japan recognize the threat from 9.2-inch County-class cruisers?

As quickly as it recognized the historical 8-inch Counties, beginning with their construction rather than waiting to see their guns in action.

An 8-inch County was a threat in an 8-inch cruiser world, and a 9.2-inch ship would occupy the same position under a higher limit. Japanese planners would have to account for a new cruiser built by a professional navy whose capabilities they respected. Its expected crew and competent employment would matter along with the guns. The need to develop a countermeasure would begin when construction revealed a likely wartime opponent.