Any time you get new live rock that is not transfered over in a bucket filled with saltwater, you should consider quarantining it to make sure there is no ammonia/nitrite spikes and so that you can observe any nasty creatures that it may contain such as mantis shrimp.
Once you know that it is fully cycled and that there are no pesky creatures - then you can move it to the main system.
At least, that's how you should do it if you want to be careful.
If it was me - if it was fully cycled, I'de just throw it in my tank and cross my fingers. It would also depend on how much live rock it is compaired to the volume of my tank.
Anyway - home that helps.