You can start transplanting right after germination and move seedlings while very small with little or no root disturbance. Gentrly loosen the soil under the roots and prick out individuals carefully, lift by the leaves, not by the stem or you can crush the stem. Transplant into prepared soil being careful to plant at the same soil depth. Do not cover up the stem. Gently firm the soil over the roots without crushing or bending the plant stem. Water gently to not dislodge the seedling....this may be accomplished easily by placing the container of the repotted seedling into a tray of water and allowing it to soak up moisture from below.