The Halloween party usually starts on the very
first Friday in October, whichever date that is each year. Normally, they don't go by dates (for example, they don't decide, "We're going to start the Halloween party on October 1st every year") so much as they go by the days of the week and which week it is, in particular. The party always begins on the first Friday in October, and it's anyone's guess after that if they will only hold it on Fridays and Tuesdays, like they did this year, or change the schedule.
However, in 2011, if I'm not mistaken, the first Friday in October will be October 7th - and frankly, that seems rather late to start the Halloween party. So I wonder if, perhaps, they may decide to begin the party on Friday, September 30 next year?
Halloween Time (the season itself) started on 9/17 this year, but that doesn't mean it will start at that time next year. In the past, it has begun on the very last Friday in September, as well as on the next to last Friday in September. I've seen both happen. Sometimes it's an early season start date and other times it's not.
Not only did I think it was crowded when I was at DLR in early October in 2008, but recent reports have indicated that October was pretty packed overall this year. It seems that October is no longer an off-peak time of year, sadly.