You can book right up to 90 minutes before the session starts (as long as there are still spaces available). So you can book in advance to guarantee your place or wait until the day, but please note once you have booked a space you cannot change it. You can book simply and quickly using any internet, Wi-Fi, 3g or 4g enabled mobile device. 

For a walkthrough (including screenshots / photos) of how to book your sessions, click here: Timetable Guide (it is best to rotate your smartphone sidewards / horizontal for the most user friendly view).