I used to set up salt tanks in a day, add fish the next day, but you gotta find non rotton live rock, which can be, shall we say difficult. However it's totally possible. If you got live rock that's not done cycling then you're gonna be waiting a while. it's best to just toss it in a black trashcan, throw the lid on it and put a heater and a big pump in it. In not too long you've got happy live rock. Though you do wanna make sure you do a water change or two, that water can get FUNKY in more ways than one.