I think Casey's attempt at digging a grave in her parent's back yard was unsuccessful. She may have tried, but it was too big of a job so she gave up and went somewhere a little... easier.
Caylee could have died on the 16th, left in the trunk overnight until Casey could think straight of what to do, tried to bury her on the 17th, then take her to these woods/swamp near the home. The smell should be overwhelming within a few days. By that point, the body would have been there long enough for fluids to seep into the carpet... then made the flurry of calls on the 18th to see if anyone was home so she could go there to clean up the trunk. She wouldn't have done this at the b/f or bff's.. they would have asked what she was cleaning possibly.
I agree that Casey likely didn't actually bury Caylee at any point in the back yard. It would take a lot of really tough digging to accomplish that -- it's much more difficult to dig that size hole than one might imagine. The further into the ground you dig, the harder the earth is, too. Besides, surely LE would've noticed signs of the ground having been disturbed if she'd dug a spot large enough to contain Caylee's body.
I've been trying to understand and excuse the GPs because I'm so heartbroken for them, but I don't believe George's gas can stories at ALL. Well, I do believe he's truthful that Casey stole them (vs. his first story, that a neighbor took them), but I don't think she was there on the 24th at all. I think he may be trying to show that there was no bad odor or signs of Caylee having been in the trunk up to that point. IMO, he likely found those gas cans for the first time when he retrieved the car from the impound lot. That's why he hadn't ever called LE to report that the theft had been solved so they could close their case.
Why that specific date...that very specific time (down to the minute, practically)...I do not know. But this family knows more than we do, for sure, and there is a reason George changed his story. Likely the same reason Cindy changed her tune about whether they'd ever heard the sitter's name prior to July 15th. Both their "revisions" obviously serve some purpose or they wouldn't have made them public. Since it sure doesn't seem that either tale would aid in finding and saving Caylee, I have to believe they were devised to help Casey in some way.
Maybe Baez said to the GPs, "You know, LE has info about the 24th that doesn't help Casey. Are you SURE neither of you saw her or the car on that date, around say 2:30 or so?" Or "Too bad no one saw the car or Casey at any point after the first few days so that they could attest to the fact that there was no body and no decomp odor in the car at that time."
Who knows...but there has to be a reason for the fabrications (and for both of them, at least one of their stories simply can't be true). It has to in some way benefit Casey's defense. Either that, or possibly Casey told them if they say what she wants them to, she'll give more info. Sure can't think of any other reasons they'd knowingly be willing to publicly expose themselves as liars. Sure is baffling.