It depends which AP you buy that will determine your block out days. I purchased the premium AP which doesn't have any block out days.
We went with the premium because not only did it not have block out days but the discounts on food and merchandise and accommodation meant that the card paid for itself in our one two week trip.
If you do have block out days with the AP you are buying and its a time you are going and you are not really interested in the discounts for that trip then getting the park hoppers first would be a good idea.