The fact that both cities have same latitude facilitates calculations.

    We should not make corrections to account for the latitude difference . . . 



The difference in longitudes is 5 degrees, which is  of the full Earth's rotation angle.


Hence, difference in times when sunrise happens  is    of 24 hours,   or


     of an hour =  of an hour =  of an hour =  of an hour = 20 minutes.


Sunrise at Detroit happens 20 minutes earlier than at Chicago, which corresponds to 6:40 of the Detroit's "eastern standard time".