When does implantation happen?

Like I know they say usually around 7 dpo BUT saturday (9 dpo for me) I had the worst cramps and thought I was going to start all day. I woke up yesterday with a LOT of creamy cm but no cramps and then today I'm back to barely any creamy cm and no cramps at all. I should start 6/4 so I don't know what this is all about...could it have been implantation that late and is it normal sounding if that's what it was?