That is a very open ended question as there are loads of variables. It all depends on his space, lighting, experience, knowledge of mediums, his current growing conditions, the amount of plants given and their strain or strains, iff I already have plants in my grow and at what stage mine and the clones are at, etc.
I hate using rockwool so I would probably try to set them, cube and all in either a hydro system, in 8" net pots filled in with pebbles. Then depending on the amount of clones and the space I have, would decide how big I let them get before fflipping them.
There are way too many variables to say anything more specific. One tip though would be, make sure the water given is well aerated to help prevent root drowning.