I wouldn't want the OP to count on seeing Halloween stuff on 11/5. There are definite start and end dates for the seasons (both Halloween and Christmas), so once the end date passes, things could disappear the next day or in a few days. There's no telling what will happen. I think it just falls on who can get what done and when, and timing. The HalloweenTime season officially ends this year immediately after 10/31. Last year I believe it ended immediately after 11/1 so things were delayed by a day. All the major stuff (Halloween landmarks) will be down (like the giant Mickey pumpkin and all the pumpkins at the turnstiles) by November 5th, I'm fairly certain.
It is probably not planned out that there will still be any Halloween stuff up - and the Halloween stuff is not nearly as thorough and park-wide as the Christmas stuff is anyway, so there is not as much of it to see or to take down. During Christmas, there is no escaping what time of year it is, because the decorations are so thorough and extensive all over DLR.
HalloweenTime is not that extensive at all, so there isn't as much to remove, but I tend to think it's just a matter of how much they can get done in the overnight hours and the time frame in which they have to do it. If they could get everything down in a faster time, I'm pretty sure there would be no traces of Halloween into November. But trying to get all the Christmas stuff up by a season start date of 11/12 probably contributes to the delay in taking Halloween stuff down - what there is of it to take down.
There are 700 Christmas trees of all sizes that go up for the holidays - in all kinds of places around DLR. I think they start putting up the smaller, less visible ones in some places first, and then they save the gigantic trees for last - but people have reported seeing the Main Street tree up a week before the holiday season began. However, I think that was when the holiday season began one week later (in 2008) than it's beginning now. In 2008, it started only 6 days before Thanksgiving, so there was time to get the trees up sooner. Last year and this year it has an earlier start date - 13 days before Thanksgiving and 12 days after HalloweenTime ends, so there is not as much extra leeway to put up the huge trees ahead of schedule.