Ok I have a friend who is about to finish his ick treatment in his tank he used the turning up the temperature and salt method. He's confused because he know's he has to do large water changes 40-50% but he doesn't know if he has to do it within several days, hours, weeks etc his 10 days is up on Saturday and he just wants to know how to get the salt out of the water

a little salt is ok for the fish he should water changes every 2 to three days to get the water parameters back to normal as you dont want to lose the cycle

10 days treatment period will compromise quality
of water unless you had a good filtering systems.
i suggest 30% in two consecutive days to avoid shock
for sudden change of environment. check water parameters,
if found normal, then continue the normal maintenance.

salt never evaporates. 30% change of water removed 30% of salt.
the 2nd 30% change of water removed 30% of the remaining 70% of salt.

never do total cleansing of your filtering system, it will
create another problem if you do that.

Added salt dissolves into the water (like sea water is salty). Doing water changes will remove it over time.

10 days is a long time to go without a water change (for oscars), so do 2 or 3 large water changes (25-50%) to get your nitrates down and then just let your regular water changes remove the salt

For future reference, if you have to do this again you can still do water change just redose the salt for proportion of water removed. Example if you added 8 tablespoons of salt and you then did a 25% water change you have removed the equivalent of 2 tablespoons of salt. So add 2 tablespoon of salt after the water change