The right answer isn’t the morning, right? If you have the freedom to shower at anytime and showering is the classic case where lateral thinking — or magical problem solving — happens you should shower when you have a problem to solve. Of course, there’s a point at which not showering becomes embarrassing. My wife might argue that we’re already there when I’m not showering first thing in the morning but I’ll give a cutoff time of after lunch. So the answer is threefold: when you have a problem to solve but no later than immediately after lunch unless you have a spouse in which case the first two criteria are overruled by whatever she tells you.