If you are a garbage collector, then by all means, shower at night. But otherwise, showering in the morning is where it's at, especially if you do anything creative.
"[If] you are a creative person (or need to be creative for your job). Taking a shower is a lot like meditating, because you enter a relaxed-yet-alert alpha brain wave state — a state that’s perfect for coming up with good ideas. This is why it’s best to take a shower at the beginning of the day to give your brain a kick-start, Harvard psychology lecturer Shelley Carson explained to Greatist."