It takes about 4 weeks after the last spot is gone from the fish to completely rid the ich when using hyposalinity. It'll take the main tank about 6 weeks, with no host, to completely rid it of ich. I know it sucks, I'm on week 3 and it's taking forever it seems!
I'd be careful with the wrasse; they aren't very tolerant of "freshwater" conditions, i.e. low salinity. I wouldn't go any lower than 1.008. That's how I killed mine
Hyposalinity is pretty relaxing for the fish - but I wouldn't continue it for longer than necessary lol.