We have a tank with platys at SG 1.005 to 1.006 and they live there now over 8 months and many young have grown up in there, too.
Brackish water fish don't need a special acclimatising as they can move between different salinities within minutes. So, acclimatising them as normal is sufficient.
The only reason to stay within a given salinity in a tank is the fact that the nitrofying bacteria need to adopt and they do that very slowly. That means, changing salinity from freshwater to brackish SG 1.005 or vice versa could take a week or a month depending on your tank setup.
PS:
I used always marine salt to make brackish water. That's the proper way and I have no clue if other salt would be suitable, too.