@barclay.
My son and I have always arrived between 4:30 and 5:00 and have always scored the autographs we wanted. Last year it was a little close for Ray Park and for John Ratzenberger. As this becomes more and more popular, you have to start earlier.
I found the difficult part is if you are lined up outside of the bag check. In front of the bag check, they check you prior to bag check opening. Outside the bag check you can get shuffled back sometimes.
Everyone in line is great because we are all there for the same reason. If you have to break line to use the bathroom everyone will hold your spot. Sometimes things get a little iffy if a group goes to the front to join a single person saints in line.
@yulilin3 has much more experience with this and can shed more light on it than I can.