The liverock has the bacteria to do the cycle which is why only that takes a liittle longer. You can use the shrimp but place it inside a mesh bag, like one you would use for carbon, so it doesn't get lost in the tank.
Even with that method you want to make sure yur parameters are correct for at least a week prior to adding any inhabitants.
The cycle will look like:
Ammonia, Nitrites and Nitrates will all read 0 at first. As the cycle starts, you will see a rise in ammonia while Nitrites ad Nitrates may not register. The second portion of the cycle, the ammonia will drop slightly and you will begin to register Nitrites. The third part of the cycle, ammonia will drop to 0, NItrites may or may not register and your nitrates will spike...this is going to signal the end or near end of the cycle. You will need to do at least a 50% water change at this point and then watch it for another week. Your ultmate parameters should go back to all zeroes although NItrates dn't always go completely away. You want to maintain Ammonia 0, Nitrite 0, and Nitrates below 20 ppm
if you are fish only..if you start to add corals Nitrates should be as near 0 as possible.