In the post announcing Dark Harvest, nick states that it ends on November 1st.
However, when you look at the description for halloween candy, it says it expires when Dark Harvest ends, and then it says it expires on November 6th. Which one of these dates is correct?
Probably it will be just like last year, the event itself ends at November 1st but you can still trade your candies for prizes until the 6th (I don't remember last year's date, so I'm comparing to the "after the event ends you still have some time to trade tokens").
It maybe will end when the missions change as i checked the missions on the 1st and the The Dark Harvest mission is not there. I'm not sure what time for US users, however i think i know the time for it EU users. The missions here in England change when it hits 8.00AM.
Probably the 1st, but the vendors might stick around until the 6th.