Ovulation “should” occur 12-48 hours after surge, but Opks do not determine ovulation, they just detect an LH surge. Without temping to confirm ovulation you don’t know if or when you truly ovulated. Just by opks the 12th would be considered “ovulation day” then 1DPO is the 13th. So also depends on your luteal phase length. But period should be around 14 days after ovulation. But again, without confirming ovulation we don’t know if you ovulated or not.