Check out the FAQ's and ebook which will explain all you need to know.
To TTC Girl the 12 hours is just a reference point. For a girl, it is 12 hours from Ovulation NOT positive OPK but you have to pinpoint when you ovulated. Usually we ovulate 12 - 36 hours after positive OPK but it is more important to watch for signs such as your CM changing from EWCM to creamy etc then you DTD. The info in FAQ explains all.
I think Gl meant good luck.