For playing a city game in 's-Hertogenbosch, April, May, June, July, August, September and October are usually the nicest months. The weather is often better for walking outside, the days are longer and you have more room to explore the city at a relaxed pace.
In spring, the city centre often feels fresh and lively. In summer, the long days are the main advantage, although it can be busier. September and October are pleasant if you prefer a quieter outing and still mild temperatures.
Outside this period, it can still work well, but the experience changes. In winter, comfort matters more and you need to take rain, wind and short days into account more often. That does not make a city game less enjoyable, but it does make it a little less relaxed.