When does implantation bleeding occur?

I had implantation bleeding with a previous pregnancy but I wasn’t trying to tracking at the time. My period was due yesterday, and yesterday afternoon I had a little tiny bit of pink when I wiped. I thought it was just the beginning so I put in a tampon and to my surprise it had a little drop of pink on the top. Literally almost nothing. So I shoved some toilet paper up there to check and nothing. I tested a few days ago and it was BFN. When does implantation bleeding happen?