if you arrive 2 hours prior, you can be turned away. this was told me direct from cbp, and etihad, but that is up to you.
As for my ticket, I showed up exactly 2 hours prior to my flight, and was at the baggage drop off. I was turned away due to not being more then two hours.
I ended up having to book new tickets via gulf to baharain, to london, to chicago.
plus another added night in dubai.
In dubai's customs, i was through in under 30 minutes.
Even when i landed in chicago, got my normal "random" security screening(have global entry) made it through in under 10 minutes
as for people missing flights in abu dhabi, i was with about 10 others in the same boat.
I helped them book similar flights as to what i booked, so that was nice.