Thanks for the replies.
We know what nights we can do, so I think we will grab them now.
But as you say Julia, if we feel that a night is going to particularly good, we can buy more when we are out there.
We want to buy them now so we can book a place at the Liberty Tavern that way we can stay there while they clear the park.
Really looking forward to it! we've been there and done this a few times now, but this will be the first with our 4 yr old. Pity we can't do Halloween Horror night at Universal, that is by far and away my fav' out of everything!