How much roots is good for cloner?

When do you guys take your clones out of the cloner?

When is it safe to put the clones in soil? How much roots do you need?

Thanks!

2-6in is when i pull them a put them in soil. i use cheap styrofoam cups, and line the bottom quarter with wet soil, then put the clone in delicatly dropping the roots to rest on the layer of wet soil, then i back fill with dry soil for rest of the 3/4 of the cup.. thats about all i do..