Time frames are dependant on a cuple of things, the first is temperature, but the one that typically frustrates aquarists is the fact that we really don't know exactly when the last freeswimmer attached. The freeswimmers can't be seen, and slowly grow to a visiable size so they aften show up and linger after treatment has started. In most cases 4 days is about when they start dissapearing off of the fish but it can go a few days longer. The other major variable with meds is timing and dosage strength. The meds effectiveness has a direct relationship to dosage, time, and organic levels in the tank. It is possible ( maybe even probable) that some free swimmers will survive the meds long enough to attach to the fish and protect themselves. So you may actually go through a couple rounds of the battle before you win the war. The only time I would be concerned is if an outbreak worsened after the first 4-5 days of treatment. Salt is a little more dependable, but there is always the long shot that a freeswimmer could find a host quickly after hatching, and get attached and survive. This is the rreason we say continue treatment for a full week after the last sign of ich on your fish. Every once in a while it takes some extra time for all signs of ich to be gone.
Either way, just relax, stick to your decided system, and wait it out. Your fish wil be better off in the long run.
dave