The internet is a magical device. Unfortunately in this case, it wasn't. Keep checking the WDW website for hours of operations, probably in a couple months.
Hours tend to be short. 9 - 9 on Epcot is pretty much a given. 9 - 5 or 6 for AK weekdays. And generally, MGM and MK are closed by 9 as well on weekdays, 6pm on Halloween Party nights. I would say 9 - 8ish for MGM normally. MK maybe 8pm or 9pm. Longer on weekends, not necessarily by much.
January hours seem longer this year than before (the parks seem busier each year in January too), or I'd say to look at January for an idea on September. But really, the late August and September time period is the slowest time of year, and will see the shortest park hours.