There is no single correct time. The bar is designed as a convenient snack, and the product is positioned for three everyday situations: during the workday at your desk, while traveling or on the go, and as a small bite after training.
For a desk snack, it is useful because it needs no preparation, can be stored in a drawer or bag, and gives a sweet break without being a full meal. As a travel option, its 40 g format is compact and much easier to carry than a pastry or an open chocolate bar.
After training, the appeal is different: it is a sweet snack that contains protein and added fiber, so it can feel more substantial than a plain candy bar. The product is not described as a specialized post-workout product with specific recovery effects; it simply lists after training as one common moment. If you want something sweet after exercise, this bar can be a practical choice.
The broader idea is to use it in place of less balanced sweet options. If you know you will want something chocolate-like and caramel-like during the day, keeping one bar for that moment can help you avoid reaching for standard confectionery.