My own timeline from what I've been able to gather from news reports and interviews:
On Saturday, July 12th, Cindy and George Anthony received a notice from the post office that the post office had tried to deliver a registered letter during the week, and the letter was waiting for them at the post office.
Monday, July 14th or Tuesday, July 15th - The Anthonys go to the post office and get the registered letter.
Tuesday, July 15th, George and Cindy go to the impound yard and retrieve the car. George drove it home and in one report said the car stunk and he had to drive with the windows down and had nausea.
When they got the car home they found a slip of paper with Amy's phone number on it. Cindy called Amy asking where Casey was. Amy said that Casey was at Tony's apartment. Cindy picked up Amy and Amy guided Cindy to Tony's apartment.
After Cindy picked up Casey and learned that Caylee wasn't with her, and according to Casey was with the babysitter, she drove Casey to a police station with the intention of having her arrested for credit card and car theft. Cindy found that the police station was closed and made a call from her cell phone, in which she learned that the police station she was at, closed at 5:30pm. So, we can assume that they were at the police station at some time after 5:30pm.
Cindy took Casey home, and it was another 45 (?) minutes before Cindy made the second 911 call. It was some time later that the third call to 911 was made.
In the interview George and Cindy Anthony did with Greta, they said the police were there all night, 5 policemen/detectives, with the last one leaving at about 5:30am on Wednesday, July 16th.
Wednesday, July 16th, about noon, police picked up Casey and asked her to take them to the apartment of Zenaida Gonzolas. Later that day, after Casey led the police on wild goose chases and lied, she was arrested.