I've always cloned my plants as soon as I can tell their sex after going to a 12/12 light cycle. Never had any problems. Of course, the clones are retruned to 18/6 light cycle. This time around, I cloned my plants just before going to 12/12 which means I don't know their sex yet. Of 30 clones, only one didn't survive. Trouble is, I have to colour code each set of clones together with their parent plant so I will know which are female when the parents start showing their sex.

I hope this answers your question, but I suspect it is similar to what your book says as I follow a book too.