Er, there's a much simpler explanation. Like many of the random events in PD, the Investigation robot probably depends on some variables that are completely non-obvious. In other words, something in DarkLight's method of doing the level makes the robot go slower; and it could be very specific and seem totally unrelated. That's one of the problems with going for PD times.
Other examples are things like the President in Crash Site (some methods of going to the UFO after rescuing him make him go consistently faster)... the technician in Rescue Agent (there's no reason for the updated strategy to make him appear there more often, but he does!)... the bridge in Attack Ship (what the hell IS it about that strategy that makes the bridge sequence go 20 seconds faster?)... the list goes on.
DarkLight, I recommend you shake up your routine a little. If you take your time placing the CamSpy, don't; if you don't, do. Try walking slowly down the experiments hall instead of dashing to the robot. Try arriving early and late for the robot. Anything could work. I seem to recall that opening doors for the robot did NOT get me better times in general, so try not doing that.
Then again, considering I haven't played in months, my advice may not be worth much.
