We were given a rock garden planter that the owner had once filled with a dozen or more specimens. When we got it, it was reduced to three: A thyme, a draba that blooms with yellow flowers in early spring (D. condensata if the tag is correct) and the pink-flowered fellow whose pictures are attached. The pictures show the whole plant, a closer shot of the foliage, and a close-up of the flower and fruit. Its flowers only open in full sun, usually during the hottest part of the day. While the draba and the thyme have kept to their spots, this guy has spread, taking over most of the planter. Can you name it?