Question about Growing African Violets from Leaf:

I have finally had success with starting a new African violet with a leaf.  Please tell me... when is it OK to remove the parent from the baby?

Answer:

I suggest that you leave the new little babies (there may well be several of them) to attain a reasonable size before separating them and planting individually.

When the largest leaves are about the size of the top joint of your thumb is a good idea. The plantlets will then have no trouble in growing on in their individual pots.

Chapter 11 of "African Violets for Everyone" has a full treatment of the subject of propagation of African violets.