How late in the game can you get implantation bleeding?

I'm on cycle day 42, had no period for the month of March. (af was due by the 20th)

And then after messing around at work doing squats today, I went to check my liner and had a dot of soft pink with cm.

Stuck wearing them, due to alot of cm.

But this has never been the start of a period for me. It always starts heavy/dark! So this is weird for me.

But shouldn't implantation bleeding take place before af is due? Or can you have a late little attacher?

I've tested around every two days, and all negative!