I recently read a 1998 article out of the Botanical Journal of the Linnean Society about factors affecting seed yield of Cypripedium pubescens (I don't know if this species is close enough to yours to merit action). They tested pollen germination on sucrose solution of several plants over a 16 day period. All the genets tested reached their maximum documented pollen germination between 4 and 8 days after the flower opened.