All I see in JG's statement about the conversation on the 16th is that it was "not unnormal" to hear Caylee in the background "whenever" he talked to KC on the phone. He didn't seem to have any particular memory of hearing her that day. The thing he was really sure about was that he heard her on the 24th--but that's the one he backed off from later.
I think we should keep this in mind. If JG didn't hear Caylee on the 16th, she might have been dead before KC even returned to the house. Let's say they left the house 12:50 as GA says, and he didn't go to work until 2:30. KC wouldn't feel comfortable going back without leaving at least a little "cushion" of time to make sure GA was really gone. So did she really sit in the car around the corner for 2 hours before going back to the house? If so, did she run the A/C the whole time? Or maybe she parked somewhere, Caylee was napping in the car seat, KC wanted to talk to friends on the phone and didn't want to wake her up (because that would trigger annoying mommy duties), so KC got out of the car, leaving Caylee in the car seat in the heat...then discovers a little after 3 pm when she gets off the phone with JG that Caylee is unresponsive. KC rushes back to the house to see if she can revive her (but doesn't take Caylee's doll in with her given the circumstances), calls mommy the nurse when she can't wake Caylee up...but at some point realizes Caylee is too far gone and it is really HER FAULT so she will be in trouble with parents, police, etc., PLUS everyone will know she has no job...and since Caylee is dead anyway the best thing to do is cover it up.
What do you guys think? If I knew for sure there was a chloroform search pre-6/16, I might revise this theory to something more premeditated, though.