From what they said last week, 30 is the max they can get into the room per show. The "wandmaker" picks one person to test the wands and ends up having a wand "choose" them. It's usually a child. (Last week he chose siblings so it seems to be more than one on occasion). If you're among the last people in, you're in the back of the room and he can't see you, there is pretty much zero chance that you will be the choice.
If you don't get chosen (and waiting around outside Ollivanders all day is not my idea of fun in Harry Potterland) and you can get into the wand shop, they can help you match up a wand to your birthday. Or you can choose a character wand. (I bought Sirius Black's). Character wands are also available at an outside kiosk near Hogwarts or in the main IOA store near the entrance/exit.