since the OP said they were flying on UA85, Id say 2 hours max, as long as you know you dont fit the profile where they will want to do a good checking. Also its sort of dead at that hour as most flights to Europe leave in the 4-6am time period, with the 2nd main period being 4-6pm for the night rush hour to Europe

its so dead that the Dan lounge in B is closed with a sign saying head over to C. UA usually leaves from C but if it arrives way early or late the 84 ends up pulling into the B gates.

Personally I usually get there @ T-90, never had any problems and I usually have some time to jump into the lounge to boot. But I dont want anyone else to do it since everyone is different and unless you know you wont be questioned you may miss the flight