We arrived about 8:30, the plant in center stage on the picnic table with 5 flowers beginning to open. By 11:00 they were fully open and the air scented with their perfume.
They've had this particular plant for about thirteen years and most of the time it's an ugly thing. Gangly stems and leaves, turning dull brown in the winter. It is a member of the cactus family and is native to the Sonoran Desert.
But one night each summer, in June or July, its flowers open as night falls and then close forever with the first rays of morning sun.
Here is a time lapse video of the flower blooming.