I'm not really sure that it's possible.
The Communists were mainly just a subsect of the KMT and didn't even match them in strength for that long.
The Communist forces were completely broken by the KMT in late 1935, and would be finished off in the spring of 1937 with the taking of Yan'an, so I guess it would have to be before then.
I honestly can't really see any of the communists achieving what Chiang Kai-shek was able to with helping the United States defeat Japan in 1944 and succeeding at getting China on the Security Council alongside the United States, Soviet Union, Britain, France, and India. It took a lot of lobbying and string polling with people who also believed in a degree of democratic values. I can't imagine a communist country getting that seat.
But if they were able to, the Communists were much more peasant and farmer based in their support, so I could see land reform coming way sooner than the late 50s. This would probably put the KMT plan of "A Province a Month" industrialization on hold, if it happens at all. For those who don't know, "A Province a Month" was a program where China would use a large part of its budget every month to go towards repairing infrastructure and building new roads and factories in a different province. It started in 1945, right after Germany surrendered and the Second World War ended, and kept going until 1966, touching on many provinces more than once. It's largely credited for China's industrial boom in the 1980s, which followed Japan's boom in the 1970s, and is said to be one of the main reasons that there are two superpowers in the world today, with India's rise on the horizon.