When I did hypo, I put my fish in the QT which was at the same salinity as the tank they came out of. Then, I used water that was lower salinity than their water and I dripped it into the QT tank with airline tubing with a knot in the end. This will slowly lower the salinity so that the fish are not shocked. It should take about a week to lower salinity from 1.024 to 1.009. For example, their first day in QT they were at 1.024, after I let the water at 1.015 drip in all day, the salinity had gradually lowered to 1.021. Then I kept up this process until I got to 1.009.
I hope you have refractometer as this would be nearly impossible without one!