you could also buy the uncured rock and place it in some plastic bins at home with a powerhead and skimmer running. If you would like some of the light loving critters to not die off, you also put a light over it to give some light until it is ready to put in the tank. If you let the live rock cure outside your main display, you can observe the critters that stowed away on it and make sure there isn't anything hiding that you ultimately don't want in your main display, like mantis shrimp. Once the rock has cured and stop with the die-offs, then you can put it in your main display. It is really all a matter of preference. Either way there will be some die-off, and there will be a cycle to go through. Also, if you want to know if the rock you are getting from the store is pretty much done with it's curing process, smell it. If it smells yucky, then I wouldn't put it in your main display yet. If it smells like ocean, then it is ready.