Late Implantation?

Allison • Married April 2014, TTC #1
What is the latest you have noticed implantation spotting and temp dip? For me on Cd16-18 I noticed pink and brown only when I wiped. The next day it became a little heavier and required a tampon but I only had one filled by the end of the day. (Sorry for TMI) that day my temp dropped below my cover line so I thought I was starting a new cycle but today my temp is back up to the same temp on CD18. I've never had a period this light. I think it is already done this morning. Could this be implantation this late or am I just holding on to hope that Im pregnant?