If you want a useful answer then you will need to explain how you are travelling and by what route. However, if you plan to fly by direct flight to Europe and have a quick connection to a direct flight to an airport in Michigan, then you can think roughly in terms of 12-15 hours. This could easily extend to 20 if the connection time is longer en-route. I do not know if there is a direct flight from Nigeria to Michigan, but presumably you can check online.