Fitness belongs to strenuous exercise. In order to make digestion go smoothly and avoid some physical discomfort such as abdominal pain, it is best to do it after meals 1- 1.5 hours. If it is only a light activity, it can be done half an hour after meals.
Besides porridge, it is suggested to add some other high-quality protein, such as eggs and nuts. Otherwise, eating porridge alone in the morning can't guarantee the fitness effect and the energy needed for daily activities in the morning.