Only once you have a decent quality product, however long that takes. It doesn't have to be perfect, but having something can show them what they might get out of it all.
You wouldn't get a mottled silkie right away in the F2 generation. The comb, skin color and general body shape have to be correct for that. You may not get a correct comb in the F2 generation.
Orrrrr you could just.... you know... use stock from an already existing line of blue egg laying Silkies....
https://www.backyardchickens.com/threads/silkies-that-lay-blue-eggs.1255052/#post-20137987