I want a China visa for internal meeting at Shanghai

I want a PRC entry permit for the workshop at my Shanghai office. Currently I am in Pakistan and Pakistani national. I have invitation letter from my Shanghai office. Please advise how long it will take to get the entry permit? Because my Shanghai office saying that invitation letter from Chinese foreign ministry is also required and that letter will take 3 weeks.
Can you please confirm time line of business M type for PRC if I am in Pakistan?