If they follow last year's model, the latest for BoG is around 6:20. If they do the same and you're looking at a 6:30 or after time slot, there should be a notice somewhere during the booking of the ADR that a park ticket AND special event ticket is required.
As to the calendar you're seeing, I don't know where they got their hours. There are no December 2017 calendars out yet; November hasn't even been released. My guess is they are basing it on last year, so you need to keep an eye out for what happens this year.
You need to go back into your reservation and see if they have added any verbiage about needing a special event ticket. That is later than they were allowing last year. . However, up until last year, they allowed ADRs up to 7:00 for anyone, and once you finish dinner, they escort you out of the park if you don't have a ticket. Make sure you use the restroom before you leave the restaurant, because they will not let you stop for anything, including shopping on Main St.