Any pre clearance flight closes 2 hours prior to departure. I would show up no later than 1:35am. After that point, luggage will no longer be accepted and a boarding pass will not be issued without supervisor approval. I personally had the limo pick me up from Dubai Internet city / Palm around 12:00am ( they wanted to come way, way earlier, I said no) . Arrived at AUH at 12:45am with PLENTY of time to spare.

If your passport has been registered with e gate will will take minutes to clear UAE customs. Its mandatory to register for the egate if you are departing AUH. As a guide, I would go to the pre clearance area 1 hour prior to departure, if you have Global Entry. 45 minutes would be pushing it.

The folks at Etihad are over zealous to get people to go to the pre clearance area early, I had to insist that it would literally take me minutes to clear. ( managed to squeeze in a last minute spa appointment) and mozy'd over there 60-45 minutes before departure. There were no lines. There is no incentive to go early, its full of pax, 500 of them !

If you don't have e gate registration and global entry, or flying economy add extra time. Then you have to show up 4 hours before.