1st question, you match temperature and PH, then put the fish in for between 3 and 5 minutes monitoring for stress. Take it out and back to it's place.
2nd question, no it doesn't. If what you have is in fact ich, the parasite is in the system and will survive there for as long as there is fish in it.
There are 3 methods that work: hyposalinity, copper and tank transfer method.
IF in fact your fish has ick a freshwater dip might actually stress them to the point where they become much more susceptible to ick and might actually do more harm than good.
Good luck
Leave your QT at Hypo Salinity levels. Is it a cycled QT?
The freshwater dip works, but it will also stress the crap out of the fish, this is not something you want to happen, part of the reason it has Ich, is because of stress.