Leaving the treaties in 1929 would start an earlier naval race

What difference would Japanese abandonment of the naval treaties in 1929 have made?

It would probably trigger an earlier British and American buildup while forcing Japan to confront its own shipbuilding limits sooner.

If Japan abandoned the treaty system in 1929, Britain and the United States would probably begin major expansion around 1931, creating severe pressure on Germany and Italy only a few years later. Japan could pursue larger ships or torpedo cruisers, but it would also confront its limited shipbuilding infrastructure earlier. Freedom from treaty rules would not automatically benefit the state most eager to leave. Industrial capacity would determine how effectively each navy exploited the new race.