If you have a couple of weeks before they go into the DT, I'd spread the salinity increase over the course of 10 days or so. Not sure how how much higher it needs to go, but I would think 10+ days would be plenty enough time to slowly increase it with minimal stress. 2ppt seems like an awfully large increase in one day. You can lower it that fast without any issues, but you must raise it terribly slow. Better safe than sorry...