how soon can i FIM?

After reading about fim'ing im looking forward to trying it out, but im not sure as to how young my plant can be or how old it should be? any advice?

its to my understanding that FIMming can be done at any time thought the vegetative cycle. its the seedling/clone and flowering phase that should be avoided... I have just recently attempted FIMming after the 4th node, and the plant showed little to no stress and has been growing just fine