I think most members would agree that the best / most sensible option would be to skip agencies entirely. The only exception perhaps being if there is a certain agency exclusive girl you wish to meet - or the punt is likely to be late (most AW girls seem to shut up shop around 9pm).
Given that you have time to arrange the punt, take a look at threads such as 'best punts of 2014', etc. Not only can you find a guaranteed success from among the popular girls, but you will also save plenty of £ to boot.
Why book an agency girl for an hour when you can often find a LOT better on AW for half the price (or even less than half the price in many cases).