Hmmm... It's a tough one! As there isn't another cycle to compare it to, I'd say you have possibly just ovulated on Cd20 or CD24. You get full ferning a couple of days before you actually ovulate. You temp seems to omfirm this. wait a few days and if temperatures stay up, I'd say you ovulated on CD24.

I noticed you hadn't used the saliva microscope between cd17 and cd20. You may have had full ferning there? in which case it could have been cd20. Sorry, that wasn't much help!