The advice you have been given is incorrect. There is no need whatsoever to turn Spotlight off even temporarily. Just prior to the cloning you should check that indexing of your boot volume is not occurring - simply because the competition for CPU will slow the cloning down. Just click on the Spotlight symbol at the right hand end of your menubar to see that you only have the text entry box.
Also, there is usually no need to have a clone indexed, and so you should put the target volume into the Privacy tab of System Preference / Spotlight -- that will ensure that your target does not start to be indexed during the cloning and that the target volume does not become indexed later. Should you ever need to work on the clone and want it to be indexed, just remove that volume from 'Privacy'.
Ignoring any references to Carbon Copy Cloner, see
http://forums.bombich.com/viewtopic.php?t=14531.
Andreas