The above posts were spot on in general, but I thought I might mention a few other factors to consider:
1. What do you plan to do with the 5 seedlings after you take your cuts, presuming they are all female? If you are planning on bushing them out, then top cloning them as soon as you get some nice 3-4 inch lead shoots will be fine. That would be when the total height of the plant is about 8-10 inches. You'll want some tightly-spaced nodes on there for placing below the top of the rooting cube or rockwool block.
If you are going to pack them tightly together and flower them as single colas, then you will want to wait for some undergrowth to grow out and then clone it, leaving the apical meristem (lead shoot) intact.
2. Also, just consider how much vegetative growth will be left after cloning. You want to make sure you don't chop too much or youy may stunt the plants that you are cutting from.
CM