I was there last year for NYE and "strategically" planned that particular day for AK. We stayed at the Poly and had FP for the safari that morning between 9:30 and 10:30. Got to the bus stop around 8:40 and the bus didn't show up until 9:25 and still took about 20 minutes to get to AK. (I'm the designated Disney planner for the family and, yes, I was freaking out!) The bus stop itself was packed with people trying to get to HS too and they had taken on extra buses! Getting back to the resort around 2 was tricky as well as they couldn't use the main entrance into the magic kingdom as the entrance to Magic Kingdom was all the way to the entrance ramp!
I had expected traffic issues that day but thought it would be worse in the later morning/day - not that early! I would think earlier might be easier though but somewhere around 8am is when things start getting nutty!