Question about implantation bleeding

Does this usually happen right before /during when you're supposed to have your period? If not, when would it usually show up?

Also, is implantation bleeding usually brown/pink?

A little worried here. I have a copper IUD but am a bit late on my period and have been having brownish/pinkish discharge. Not sure if my period is just starting off a little slow or if I should be worried. My period has always been very irregular in timing, though.