It does vary mate, we think on our feet in that marquee.
If there's loads of people that are booked coming in, they don't lose out, but if it's quiet it is changed.
You may not have noticed the iPads but they are always there, and 100% of the booked in are entered into the system there and then. The walk ins are booked in, in the lounge. As you go through the doors of the lounge, everyone is in the same queue as such, although you do get filtered left and right dependent on where the screeners are.
Also you may have walked in on a walk in shift, in which case, there would be no ipads in the marquee.