Live rock is just rock that is cured and will have beneficial bacteria along with maybe some crabs and what not living in it. All rock that I know of is not real anymore because its against the law to take rock from a living coral reef. If you bought dry rock it needs to go in now. If you bought rock from an established tank that has a good growth of things I'd wait till its all done being cycled. If you have rock that has no growth on it it wouldn't hurt and only help. The best thing to do is ask the lfs you got or are getting it from. Because the one I use to use cured their own rock in the back. Doing that I would put it in now.
Hope this help you understand