It is a very animated place, whether at night or on wednesdays! Why? Well because the square is surround by nice little restaurants and bars and during summer it is packed!
It is a very nice market with nice food, either from Belgium or from France. It is only open on Wednesdays afternoon/early evening, but then no one forces you to leave, right? You can enjoy a "Blanche" on a terrace if the weather is nice enough!
Don't eat everything you see, you might want to save some space for the nice restaurants around the square.