My aunt is in America and has a green card. If I want to apply for a visitor visa, what are the chances of success? How long does it take to prepare in advance?

This involves kinship, including first-degree relatives and second-degree relatives. First-degree relatives include your parents, children and spouse. Second degree relatives include your immediate grandparents. Third-degree relatives include three aunts and six grandmothers, brothers and sisters. It depends on how long you have been there, whether you have financial resources and where your visa is (generally, the success rate in big cities in China is very high, such as Shanghai). I guess you're a little hesitant. Prepare for one month at most.