Hi I'm Danny - the one who makes the bookings, alongside Andy.
When we make bookings, we ensure that there is a sufficient gap between them so as to account for potential lateness as well as to give each girl time to refresh and recompose before seeing you.
If you've made a booking with us, you'll notice that we ask you to let us know when you arrive so we can check that they're ready. This is so that we can ensure that they're near the intercom and ready to let you up, and not on their phone or in the toilet. It's not because there is someone else there, don't worry
To OP and his concern - there is nothing to be concerned about. You can rest assured that she'll be fresh and refreshed when she sees you. I haven't tried personally but if it really is the case, then DFK at the door is a nice touch that she adds by herself because she can feel the chemistry.
Hope this helps.
Danny