I think having a time limit may put some people off. Im pretty lucky as i can get there early (which gives me no excuse for booking in late! sorry alan!
).
However for those who live further away, leave work later or get lifts in, it may be hard to get there on a time limit.
How about we simply move the bookng-in sheet to just inside the door? You pay as you enter and that way you have to pay before you get anything set up?
At the moment its very easy to walk in get everything going and completely forget to do it.