The only 2 choices it gave me were either Monday 8th Dec or Wednesday 10th- I chose the Wednesday.
The 'you've passed' email that they sent me seemed to be quite pushy as to booking your assessment as soon as possible, with it almost threatening that you won't be able to book a place if you leave it too long. Maybe I've just misinterpreted it, but I'd have thought that they would have ensured there would be space for everyone that they put through.