Didn't they find Amy's phone number in the car? That would put the timeline a little later - George gets home, tells Cindy about the smell, she agrees (she admitted on news video this week that both she and her husband thought they smelled human decomposition).
They don't at first know WHO it could be, but the person who took off with the car was their flaky daughter, with Caylee in tow.
Frantic search through the car reveals a scrap of paper with Amy's phone number. Giant relief when talking to Amy that she knows where Casey is (which makes me question whether Cindy was being honest on the stand about talking to Casey "every day" in the past month. She clearly had no idea where Casey was, if they were talking).
Cindy speeds over, picks up Casey, still doesn't know that Caylee isn't with a sitter. Stubborn Casey refuses to take Cindy to Caylee, Cindy drives to closed police substation, calls LE and is told to call again from her home.
According to an earlier interview, it was shortly before LE arrived that Casey admitted she didn't know Caylee's whereabouts. That must be what prompted Cindy's second call. Didn't Casey say LE had arrived while she was talking to the dispatcher?