The Delacorte seats 1880.
There are a maximum amount of donor seats per performance. I am not sure what the number is, but many dates are already maxed. It varies from performance to performance. Corporate donors, such as Bank of America, can receive a large block of tickets, sometimes getting a whole section.
Tickets given out really do vary daily. It depends on any number of factors: the size of the line, donors, corporate donors, staff/cast tickets, press, etc.
For this show... I would say arriving there around 8 would not net you tickets. This will be a show that you may need to spend the night in line to be guaranteed.
HOWEVER
There is a standby line that forms in the mid-afternoon. Unclaimed tickets start being given out to the standby after 7 and will continue to be given out until 8 as tickets get released.
For As You Like It, people started lining up at the beginning of the run at around 6ish. Toward the end, they were lining up at 4. Most of the time, everyone got in.
It is impossible to tell you when you should line up at this point. But there is a considerable, considerable amount of buzz for the show. It'll probably be a Hair-like situation.
"...everyone finally shut up, and the audience could enjoy the beginning of the Anatevka Pogram in peace."