How much time do I have to be in US to remain a citizen?

Actually, I think the problem is with the other country.  If you have to denounce your previous citizenship in order to obtain another one, you may run into problems.  China may very well require you to denounce any other citizenship and hand return any foreign passports to become a citizen.  The US strictly does not recognize dual citizens.  Either you are an American citizen or you are not.  If you are a citizen of another country, the US doesn't officially recognize it.  Now if you return you passport to them and denounce your citizenship, they will gladly oblige.

Hmmmm. I guess you're right. When I talked to him he was under the impression that it was the US requiring this and not China. It probably makes more sense that China would make that requirement.