Beans should be soaked in cold water for at least eight hours so that they'll cook faster, more evenly, and also to minimize the unpleasant effects that have earned them their "musical fruit" reputation.
If you're short on time, you can use your pressure cooker to "quick soak" beans in a matter of minutes. To quick soak beans in a pressure cooker, rinse and sort beans, and add them to the pressure cooker with 4 cups of water and 1 teaspoon salt for each cup of beans. Cover the pressure cooker and lock the lid in place, and bring to high pressure over high heat. Reduce heat to maintain pressure and cook for 2 minutes. Release pressure by the cold water method: carrying the pressure cooker to the sink and running cold water over the lid (but not the valve). Drain the beans, and they're ready to use in your recipe.