They bloomed exuberantly at the winter solstice (making them "Christmas" cactus) and they are blooming again at the spring equinox. I've never seen them bloom for the summer solstice or the fall equinox; they lie low, dormant, at those points of the cycle. Apparently they are very yang plants, bursting forth when yang is rising. Wikipedia says there are different seasonal versions of this plant, but mine observe two seasons. Some say they are hard to grow, but I don't do much with mine. They pretty much do it all by themselves.
I just think of them as yin/yang plants.