I've read as early as 4 too :-) but From my research it's rare, but possible
iv always been told 8-10 days although iv had 4 pregnancys and never had implantation bleeding- i guess some people just dont
The doc said I had implantation bleeding :/ and I was 5/6 weeks gone
Thats what i,m thinking. I just Google it and saw a lot of things saying as early as 4dpo.
I've never heard any sooner than 6 days personally. I would say that's the earliest it can happen.