That is a very tricky question! Some people know right up front exactly what they want and do not waiver in their commitment to a design. In these rare instances the design process is very quick however this is generally not the case.
Once we start to look at spaces and options new thoughts are generated and the plan evolves. This can take a week, weeks or months depending on how often you change your mind. Obviously my goal is not to take more than a few weeks by discussing your desires up front and getting a solid handle on what you expect. After the design has been finalized the Construction Documents generally take 3 to 6 weeks depending on the scope of the project.