Don't know if this helps but I will tell you my story -

I had a long cycle and can't quite remember what CD I ovulated but I had implantation spotting 6 DPO - pretty much the same as you describe yours. I got a bfp 2 days later on 8 DPO. Very feint but by 9 DPO the line came up instantly and was not so feint.

I worked out my due dates based on my ov date but when I had my ultrasound it said I was 2 days less pg than I thought I was which means I had implantation bleeding 4 DPO and got a bfp 6 DPOs or (as I suspect) the u/s was not very accurate.

Thought that might help you out a bit. Sounds positive what you are describing!!! Hope to hear about a bfp soon!