I had a clear BFP at 8dpo with this pg (I was certain of when I O'd and was confirmed by 2 x US!), but I agree with PZ, I think it's different for every woman and every pg. I also used First Response.

If you couldn't bear another BFN and you are very patient, wait a couple more days to be sure the result is accurate.

I have everything crossed for you Berenice!!