Ok, let me start by saying that if I'd noticed this with any other author I never would have thought twice about it. Since it's Brandon, this has me wondering a little, especially since we're going to see the events of this night from three more view points (I think).
/TL:DR My basic question here, odd as it seems, is what was Gavilar doing in his chambers wearing his plate? We lose sight of Gavilar during Jasnah's prelude scene in WoR. When last we see him, he is with his guard, Tearim, who is wearing the king's Plate. Jasnah also note's that he is returning to the party when he leaves her. /End TL:DR
Based on the description of Jasnah's activities between leaving him near the party and seeing him dead near his chambers, relatively little time could have passed by. Several minutes in Shadesmar, several minutes with Liss, and the time she spent walking off her encounter in Shadesmar. It seems to me we're probably talking about a span of time somewhere around 15-20 min give or take.
If that is correct, I figure Gavilar would have needed to return to his chambers almost immediately following his conversation with Jasnah (according to Szeth in WoK, he had retired from the party hours before, so presumably he does not return following the conversation with Jasnah). Then get Tearim out of his armor, get himself into it, and engage in a relatively long fight with Szeth in order to get dropped and impaled in time for Jasnah's arrival on scene.
So, trivial as it seems, why did Gavilar (who, as noted by Jasnah in this scene had stopped wearing his Plate lately, letting Tearim wear it instead) rush back and put his armor on? He told Szeth that he had expected an assassination attempt, but if he knew the exact timing, one would expect him to be much better prepared. If he knew that it would take place that night, but not when, one might expect that he'd still be much better prepared, AND he'd be wearing his plate the entire time, or at least as long as propriety allowed once the treaty signing was completed...
I can come up with a crackpot theory or two, but I feel ridiculous enough even asking the question. Anybody else want to take a stab at this, offer a different accounting of the timeframe, or just tell me I'm nuts?