Your university would probably know, if you can't seem to find any information.
As a part of of the ATAS Application, you will need to fill in a section outlining your course of study/research. For this, I was provided a research statement to include on the ATAS form, which I was advised to copy and paste the wording in its entirety.
For me, it was more or less an outline of my proposed research project, spelling out that ''no, i dont plan on making bombs and blowing up the country while i'm in the UK...'' I'm not exactly sure what you would put for an MBA, but since my university provided what I'd have to put word for word, perhaps yours will do the same if it is in fact, required.
As for timing-- I submitted my ATAS clearance application on 11 May 2010, and received approval on the 26th May 2011.