These are from my notes about previous years:
First Day Closed: Mon, 08/30/10; Start of HalloweenTime: Fri, 09/17/10 (Labor Day: 09/06/10)
First Day Closed: Mon, 08/29/11; Start of HalloweenTime: Fri, 09/16/11 (Labor Day: 09/05/11)
First Day Closed: Mon, 08/27/12; Start of HalloweenTime: Fri, 09/14/12 (Labor Day: 09/03/12)
First Day Closed: Mon, 08/26/13; Start of HalloweenTime: Fri, 09/13/13 (Labor Day: 09/02/13)
First Day Closed: Mon, 08/25/14; Start of HalloweenTime: Fri, 09/12/14 (Labor Day: 09/01/14)
First Day Closed: Mon, 08/24/15; Start of HalloweenTime: Fri, 09/11/15 (Labor Day: 09/05/15)
The start of HalloweenTime has been creeping earlier and earlier each year, which makes sense given its popularity. The general rule of thumb is that HalloweenTime typically starts somewhere within two weeks after Labor Day. Labor Day is Monday, September 5 this year, so if they follow the same schedule from 2015, it would mean HalloweenTime would likely start on 09/09/16. If they go back to the schedules from earlier years, HalloweenTime would likely start about 2 weeks after Labor Day, which would be closer to 09/16/16.