From as near as I can guess, about 1hr 45 minutes. Depending on the day and time you travel, it will include at least one transfer from the regional (S.M.A.R.T) bus to a City of Detroit Bus (a “DDOT” bus) and also possibly 2 or more periods of having to walk on foot ... once you are in the City the longer of which is a little more than 2 klicks, from Grand River to Columbia on Woodward, which may take approx 15 minutes depending on what you encounter.
You should do some thorough planning for both of the bus systems, and by streetmaps and printed info to avoid problems if something goes wrong ... particularly because the SMART (regional) bus customer service closes at 6pm on weekdays and 4pm on Saturday (no Sunday hours) .... and the Detroit DDOT bus has customer service operators until 6pm weekdays and no operator assistance at all on the weekends.
Be careful when riding the DDOT busses.
btw: you’ll be within about 3 minutes of the Detroit Beer Company, midway on that longer walk. (http://detroitbeerco.com/Default.aspx