When you join the Wait List you will receive an email whenever a session is cancelled within the next 7 days. You can look at the available time and if it's suitable you can book it, in which case you will be removed from the list. If it's not suitable or was already snapped up you will remain on the list. It's a 'first in first served' arrangement.
You can use this form to add or remove yourself as required and you can unsubscribe directly from the notification emails you receive.