I am sensing a sort of desperation in reading these threads and I just can't figure out the purpose of proving that Lisa died earlier than sometime Mon. night or early Tues. morning. Why would they have waited so long to report her missing? It would not take 2 days to figure out a cover story. Deb seems to be smart enough to figure out that her bout of drinking that evening would point the finger straight at her and get her accused of neglecting her children, so what was that all about? As an alibi, it stinks.
Jeremy taking a second shift that night to make sure he had an alibi doesn't make sense... if the deed was already done, he didn't NEED an alibi for that night, he needed it for the time that Lisa was actually killed and disposed of, if it did happen earlier. And I could almost bet that LE has tracked their movements for that whole weekend, even if they haven't come out and said as much.
I also believe that LE would have found an opportunity to talk to those boys by that day or the next day in a way that would appear to be just conversation and find out if they saw their baby sister at all the day before, or what they remember about the time leading up to her disappearance. It's SOP, Investigation 101... try to establish a timeline for when the person was last seen by ALL family members... even kids. Seven years old is plenty old enough to know whether they saw her that day, if asked soon enough. Sure... the parents could have coached them ahead of time, but little kids have a tendency to let the truth slip out, even when they're lying.
Sorry, I'm not buying this theory that it happened a day or two before they say it did. I see no reason to believe it, because 1) it really doesn't matter when it happened, if they're guilty, they're just as guilty one time as another and 2) I see no facts to suggest it happened on Sunday, only speculation. I don't base theories on what COULD have happened... just because it COULD have doesn't mean it DID. If LE believes that Mon. night/ Tues. morning is the timeline they have to work with... that's good enough for me.