you can bath anytime you want but if during late night i don't suggest that you take shower frequently. it should not be your night routine. i don't have any reference for that. and if you think you are all right until now even with taking bath every midnight, go on. proceed what you love to do. my mom told me not to take bath at midnight, and i trust that she mentioned about pneumonia.

some things are unexplainable through science or research, but if you have seen it by your eyes, you will believe it. plus, you don't sweat every night before sleep don't you? take shower just to clean yourself up. its no harm i suppose. i do midnight futsal and took shower after games anyway. just to clean the sticky sweat.