I find my lotus - in a pot in a heavily sunlit area - flowers about once every 3-4 months. It works in cycles, with it dying down and most of the leaves dying, then the leaves come back and then the flower comes. I use a fertiliser recommended for lotus and always try to keep the water full. Usually there is only one flower at a time, but once I had two.
Here is one lotus blooming. From start to finish it took about 12 days, but the final full open blossom only really lasts a day or two. It's always very nice though :)