Gumbo is one of those dishes that tastes better the longer it cooks as it allows the flavors to develop. If you have time, I recommend letting it simmer all day long. Ideally, it should be cooked for at least three to four hours. If you're in a pinch, you can serve it after simmering for just 30-minutes although you will forgo the depth of flavor it would attain if it cooked longer.