I had a CP back in November. I had a light positive first response on a Saturday night, nothing Sunday, Monday, Tuesday, got AF full force super heavy on Wednesday.
Blood tests were taken Monday (HCG=8) and Wednesday (HCG=4).
I don't know what CD's all that happened on b/c my cycles are irregular and I wasn't temping at that time - but my guess it was around 12 DPO when I took that first test and got a faint positive - so my AF came right around when my AF probably would have been due anyway - it was just extra heavy and crampy likely due to the CP.