The confusion may be that people tend to think of night time as the prior day, and when they get up in the morning, it's a new day. Hence the confusion of June 26th and June 27th.
Casey may have disposed of the body sometime after midnight on June 27th, and some might say is was the "night of the 26th." Casey disposes of the body in the hours prior to dawn. Certainly, disposing of the body would leave Casey reeking of decomposition, but I don't think she would have gone to her parents house to clean up. If her parents woke up while she was taking a shower in the middle of the night, what sort of explanation could she give them, and they would ask where Caylee was. What date was it that Casey took a shower at JG's?
I think Casey did go back to Amscot and pick up the car and go to Cindy's house about 10:00am on June 27th, as LP stated. Then she went back to where she buried Caylee to see in the daylight that she had not left any evidence behind. Then she returned the car to Amscot and called Tony to come pick her up.