1) I have a TC (Time capsule) not Airport Extreme. Sorry for wrong info.
2) I've changed the ethenet cable to a Cat 5e and it now ok to detect Gigbit ethernet.
3) Somehow, I think the time estimator is wrong. I am transferring using the ac network right now and it's saying 18 minutes at 36GB out of 55GB. This makes sense. I think the estimate time was wrong. I think it should be GB not MEG. The problem it gave was like 2 days at start but as it goes, it is now 15mins.