Yep, that's fine. I usually get the mix going in the evening and then leave it to sit with aeration overnight before using it. Some mixes stabilize faster than others and some brands claim to be usable in-tank in just a few hours, but trying to use it too soon is riskier than just being cautious and giving it some extra time. The water will still be a bit caustic and unstable for a while even after the salt isn't visible on the bottom anymore.