A lot is to be gained. Besides what other posters have stated, lying would remove the house as the scene of the crime. If she left alive on the 16th then she wasn't killed in the house.
But the if the computer usage indicates that she did come back to the house,
then the murder could have taken place in the home even if George did see them leave in the morning. (although I don't believe he did). There's no way that he was unaware of a fight occurring between CA and KC, so another "normal day" doesn't cut it, even if their "normal" was fighting and screaming.
Never did buy the "off visiting friends and taking a little vacation" story that CA spun, but loved this little Freudian slip...I talked to my daughter all the time and always had a good explanation of where they were at. And it made some sense. I mean there was no reason to believe