It is not the hypo conditions that make the spots on your fish disappear but, rather the lifecycle of the parasite itself. Hyposalinity is not going to kill off the ich while it is attached to the fish. Hypo prevents the parasite from reproducing once it is off the fish.
So, the spots will disappear depending on where they are at in their life cycle, not on hypo. Spots should be gone within about a wk.