Unfortunately, there have been reports that this may be in progress already... which would be completed prior to landfall. Here's hoping those reports are wrong.
It's physically impossible for Katrina to complete an eyewall replacement cycle before landfall. It's not nearly enough time. Like I said before, for reasons mysterious to me people have this incredibly wrong notion of how long it takes for an eyewall replacement; it's on the order of 18 hours.
Camille hit over Biloxi, so this will be much worse. My parents both grew up in LA and compared this more to Betsy. Mom was only about 6 when Betsy came through and vividly remembers it.