DLR doesn't generally release the start dates of the holiday seasons until sometime in the summer. HalloweenTime has been starting in early-to-mid September for the last several years. The start dates have been 09/17/10, 09/16/11, 09/14/12, 09/13/13, 09/12/14, and 09/11/15 for the last few years. If I had to guess, I'd say 9/9 or 9/16 are the most likely dates for 2016. As theluckyrabbit said, the end date is most likely 10/31 (especially given it's a Monday in 2016).
The Parks Blog announced the dates for the holiday season on September 3rd in 2015 (it started on November 13, 2015). For the last few years, the official start date has coincided with the Avenger's Marathon weekend, so if that pattern hold true November 11 is the most likely start date for 2016. Unlike HalloweenTime, there is something of a rolling start to the Holiday season. Some of the holiday offerings may start a week or so before the official start, but we won't know more until much closer to the date.