I don't think the castration police will come and check on you if you ring Soay later than your 7 days window. Soay testes are tiny and pop back up quickly. I see it as a welfare issue to ring too early, as the ring being the size it is, there is a likelihood that even if you get it on, the testes will slip back through it, or part way through it, which would be exceedingly painful. Back when we kept Soay, we did on occasion not ring until 3 weeks, with no noticeable pain to the lamb.