My question is regarding ovulation and conception, let me preface by saying i'm 31 with three children and while I know many things about reproduction this has confused me.

I had a long cycle just pass I ended up being 5 days late and in an effort to determine if I was pregnant (i am not) I took both a pregnancy test and an opk. The opk was taken by accident due to similar packaging. I was on day 31 of a normally 28 day cycle. It came back as obviously positive. Because I was surprised by this I took two more throughout the day to be sure of the result and sure enough they were positive. I also had plentiful ewcm. Still no period the next day. Took another opk and it was clearly neg. Finally started cycle, 3 days after positive opk. So here's my question if in fact through some strange quirk I did ovulate on or around cycle day 31 and had unprotected sex around that time could I still concieve, considering that fertilisation takes place in the tubes and takes anywhere from 4-12 days for implantation to occur. I am on my period right now but I guess what i'm asking is could fertilisation occur in the tubes while on a cycle and if cycle passes quickly then have implantation occur.

I imagine it's unlikely but I was very curious and was hoping you could give me an answer to my lengthy and weird question