killing everything off is "cooking".
cooking can be done fast, say a couple days. It is the die-off left on it that makes it unsafe to add to an existing system. You could kill everything on it fast, and add to the tank immediatly if it was a new system.
I am guessing your tank has been up and running for at least 9 mo.. you could add a small amount of uncured rock to the system, but no more than your bio can keep up with.