keeping an unusual vigil

Last night, until way past my bedtime, my mom and several sisters (plus a niece) kept vigil for a plant: the night-blooming cereus. My sister Nell has two of these plants, which flower only once a year (evidently with only one flower per plant), and that at night. The first of her plants flowered and withered the previous night, and she didn't want to miss her last chance. The flowers are truly stunning: petals about four inches long, at first closed tightly in a white football shape. When we got to the house, the petals had begun to separate, leaving a dime-sized opening in the center of the flower. By 10:30 I had to call it quits. The flower by then had opened to almost three inches. Nell tells me that the plant opens fully, and almost as soon as it does, it begins to close and droop. I found a time-lapse image of one on Google: here's the link.