I'd plant them in the ground now and not wait for fall. Take them out of the pot and plant them exactly as they are with the tip of the bulb (right below the stem) 6" beneath the soil line. You can cut off the "candelabra" - the little arms where the flowers were attached - to prevent wasting energy on seed production, allowing the bulb to feed itself off the stem for the rest of the season. Let the foliage turn yellow, and eventually brown, over the course of the summer and fall. Cut the stems down in the late fall when they're dry and woody. I usually leave an inch or two sticking up so I know where to look for them in the spring and don't accidentally dig or plant over them.

The "dying back" period sometimes isn't the most attractive for lilies so if you've got a good spot picked out with surrounding plants to sort of camouflage them, that would be ideal.