You can either soak the oats in the milk overnight in a lidded container or you can leave for at least 20 minutes (or as long as you can). The overnight method will result in a plumper, more creamy oat flake and may be easier on the digestion.
When you are ready to serve, you can either gently heat the oats to serve warm or eat cold. Once you have decided, just place the remaining ingredients on top of the oats and serve immediately.