I'm around some pretty good TT riders and we spend a lot of time on it. Here are a few.
-Never start to fast - know how to pace themselves.
-Don't really feels the pain, or can tolerate it - I'm not sure on this one. My wife and son never talk about pain from a TT.
-Very good feel for how hard they are going, what they have left and how much is needed to finish.
-Pretty good VO2 max
-20min W/kg is high (duh)
-Likely not the best sprinter, but pretty good
-Likely not the best climber, but pretty dood
-Perfected pedaling for the TT
-Well fitted bike
-Good bike/equipment selection for the course (hill TT, flat, curves)
-Tend to prepare/pre-ride. But some are just crazy talented. So not all do this.