The answer to this one will vary wildly depending on the specific establishment. Some places charge a flat fee no matter how long you stay. Others charge an hourly rate. Some make it completely free. Some charge a flat fee, but give it to you an in-store credit, so it ends up essentially being free as long as you buy from them. Some charge per person. Some charge per table. You'd need to investigate your local board game cafés to see what their policy is.