I am guessing post Civil War. Some other points: No officer rank on coat so why is he being called an officer? Why the U.S. Army emblem on the case if this being said to be the 18th Mississippi, does it indicate 18th Mississippi (Union) Infantry Regiment? The wreath and numbers are not very Civil War looking to me. I am not sure how many Confederate officers I have seen in photos with a wreath and number like this.
Way too many questions about this one to make me feel that who ever wrote the description was correct.