You can go to
http://www.nps.gov/yell/planyourvisit/index.htm go to operating hours and season it will tell you what closes and when depending on weather, if you can make it by the second week in Sept, its well worth it, the elk are in rut, the leaves are changing, the bears are plentiful, there are NO crowds.
We go every year at this time and haven't been disappointed, but last year we did get snowed on the last four days we were there, we stay at grizzly rv for the first week, its pretty empty and at Indian creek in the park until it closes (it has no services)can sit out every night and listen to the elk bugle.