A good method to use for cloning is to wait till your going to feed your plants with food...and before doing so, take the clones...what happens is too much (N)itrogen is left in the shoots, and the clones will keep using it to grow untill it sucks the (N) dry...and then it will start to work on the root system.
Basiclly...all energy goes to the tops of the clones instead of going to the stem to build new roots. Some clones will not survive this so like i say...best to wait till your plants are kinda getting hungry.