Business Visa F or M

Hi I am a Myanmar national, permanent residient of Singapore, working for a Singapore Company. I need to go to China to Audit a supplier factory. I need to be there for about 2 weeks. ( at most a month). I think I need to apply for business type. F is good enough? or it has to be M? What are the additionial document that I would need to submit? ( I can submit an invitation letter). Processing time is about 4 days? Under what conditions it might takes longer?