According to pinguicula.org optimal temperatures for winter dormancy is between 5 and 10C (41-50F). It is stated that the substrate will need to be dry enough to accommodate such temperatures. They can and will rot if kept too moist during dormancy. The mid 50F's seems to be enough to induce dormancy for most hybrids and species in my collection. I reduce watering when they start reducing in size. The reduction in water does not seem to bother the plants that are still actively growing; I don't let my media go bone dry.
Link to article I pulled my information from: