They don't have evening EMH at AK any more which was usually your best chance of being in the park after dark.
There may be some late summer hours that extend into the night time.
Good news, though. In addition to the Avatar area, there is supposed to be new nighttime entertainment coming. So that means longer (after dark) hours.
"As part of the largest expansion in the history of the park, well be adding all-new entertainment experiences, including a new nighttime spectacular where live music, floating lanterns, water screens and swirling animal imagery all combine to bring a show to Discovery River that will delight our guests and truly cap off their day at Disneys Animal Kingdom. The park will introduce more nighttime entertainment as well, including live performers on Discovery Island and a new nighttime version of the Kilimanjaro Safaris."