The latest revelation regarding the timing of the "fool-proof suffication" (sic) calls to mind:
"Watch your thoughts: They become your words.
Watch your words: They become your actions.
Watch your actions: They become your habits.
Watch your habits: They become your character.
Watch your character: It becomes your destiny." - various authors attributed
As it relates to what happened to Caylee, this newest piece of the puzzle resolves a fundamental 'theories' issue for me, personally.
For the sake of simplicity, I'm abandoning my usual approach of attempting to reconcile all the available information with a theory.
IMHO...
Caylee was murdered ~7:30PM 6/16, when Casey's 'plan A' and 'plan B' attempts to hand her over for the night to Cindy, then, Amy failed. The strongest evidence supporting this is that the unanswered 7:22PM call to Amy emphatically marked the end of Casey initiating communications. After this time Casey's behavior shifted dramatically to being elusive. The last call to Amy was a very clear turning point in Casey's observable behavior on a macro scale.
Casey's actions, IMHO, weren't fueled by a well-developed plot to off Caylee. They were the result of accumulated frustrations in recent months, seemingly accelerating by the hour 6/15-6/16.
There was a stark shift in events @ Hopespring 6/16 after 2PM, as evidenced by the computer searches. The 2:51PM 'fool-proof' search coincided with the time George, who appears to have been caring/entertaining Caylee the majority of the day whilst Casey was engrossed in all-things-Casey, left for work. The search reads, to me, like a 0-100mph launch over the edge. The immediate and purposeful choice of 'suffocation' suggests, to me, putting in words Casey's desire to silence an inconsolable Caylee immediately. ETA: That George called Casey @ 3PM at the house, then on her cell is very telling that some situation was underway when he left, IMHO. From phone records, George calling Casey was a very, very rare event. To me, George's behavior in placing those calls indicates something was seriously awry when he left the house and he wanted to get an update. It doesn't seem too far a stretch that Caylee would be upset @ his leaving, and he felt guilty/responsible and perhaps wanted to console her over the phone if he could. So, there are at least two independent, observable behaviors (Casey's abrupt 'fool-proof' search & George's rare calls) that suggest things were in a drastic downward spiral by ~2:30PM.
Regardless of whether Casey harmed Caylee @ all before they left Hopespring that afternoon, the thought had become words, and the words materialized in the action of picking up the duct tape. Perhaps it was used temporarily to quieten Caylee, and then the roll went into the Pontiac as threat to Caylee; "Be quiet, or the tape goes back on!" For me, the latest computer search information seals this important means of the tape getting into the car that afternoon, to be used later. Otherwise, it seemed highly unlikely to me that it would randomly be in the car.
Casey actively sought out Cindy (i.e. flurry of calls) and hovered in the area of Gentiva after 4PM to effect the quickest possible Caylee handoff-and-escape-to-Tony's scenario. Casey was 'dressed for work' to pull of the ruse until the 'plan A' handoff to Cindy had clearly failed.
Dropping Caylee at Amy's became 'plan B', and Casey changed Caylee into her 'sleeping away from home' pajamas - the "Big Trouble..." shirt.
When meager attempts to reach Amy failed, an infuriated Casey, perhaps fueled by a fitful Caylee, used the carseat straps to restrain Caylee while she first applied the tape to quieten her (again?), then, in rage, to suffocate her as her thoughts and actions from the afternoon computer search reached fruition.
There wasn't any pre-agreed-to rendevous time for Casey and Tony that evening that we are aware of. The timing of her arrival at his apartment ~7:42PM was only paced by the 20 minutes it took for Casey to erupt, cinch the carseat straps, apply the tape, wait for Caylee to stop breathing and place her body into the trunk of the Pontiac.
Steering clear of the details, there just isn't enough information to determine with any certainty if Caylee was sedated in any way. It seems to me very unlikely, though. Casey's efforts were to hand Caylee off right up until the time she snapped. Further, Casey doesn't strike me as being empathetic, nor possessing the forethought to sedate Caylee to 'soften' the end that came so abrubtly.