what is the requirement and I many days takes for a visa to be issued?

It takes four working days to process your application. You need to provide: a passport (valid for six months at least and with two blank pages at least), filled application form affixed with a recent passport size photo and an invitation letter. If you can't provide the invitation letter, you should provide round-trip air tickets and hotel reservation in China. By the way, the original bank documents showing financial history over several months might be needed too.