I will be watching this plant very closely, because there is a possibility that it is a bud builder. At any rate, it bloomed for at least two months in 2013. The first picture I have was taken on June 30, and the last was taken on September 1. Early in its bloom season the flower was mostly rose colored, while the later flowers were off white with a rose edge.
The plant did not show any bud building in 2014, but it had just been divided, so it may show the characteristic in 2015. It still exhibited different amounts of rose and off white.
The top picture is what the flower looked like on September 1.