It would be clearer if we had the transcript of the interview. The jury will have access to both transcript and video.
"Initially", "change it", "at this point", "settled on" are all spin phrases to make it sound as if she was lying. Sounds more likely to be a slip of the tongue to me. Perhaps the interview went like this:
Police: "Where were you when Victoria died?"
CM: "Er...Harwich..."
Police [looks through papers]. "You say Harwich. What day was it? So you are saying this was when Victoria died? Can you tell me more?"
CM: "No, it wasn't Harwich. I meant Newhaven. We left Harwich and then..."
That is totally made up, but it's consistent both with the prosecution opening speech and with what happens in normal conversations or interviews - a person not having the chance to correct themselves right away because the other person has been speaking.
If I were prosecuting, I probably wouldn't try to build much on such a minor error, unless maybe they've got other evidence suggesting she lies her head off.
Regarding date of death, I wasn't wholly convinced by reports of the baby crying in the woods evidence either. Perhaps Victoria died after a not very long time in the plastic bag. Putting a baby in a plastic bag is asking for trouble, to put it mildly. Perhaps they put her in the bag, then by some amazing good fortune she was actually still OK after half an hour, and so they take her out, but the next time they decide to put her in the bag they think "This seems like a sensible way to carry her. No surprise that the squares haven't thought of it. She's been fine, so a few things put on top of her won't make any difference" - and then the next thing they know, she's dead.
^ All complete speculation.