They don't really need to be transplanted until the new white root tips begin to poke out of the rock wool. The amount of time that this will take depends on your growing conditions, root temp, humidity, proximity to bright cool light etc. Once new roots reach the relatively dry air and bright light that waits for them outside of that cube they will stop growing and your new clones could become root bound and stunted. I would say no longer than two weeks, but that is under my conditions.