This year will be hard to work out as there is an on-line entry where it used to be in person or via snail mail.
It usually fills up quite quickly – leave it more than a week and it might be full as it’ll be easier to enter (filling in forms and posting is harder than online)
You still have a week to get friends agreement, details etc and you can change details when you get there. The problem we have had is people dropping out near to the time either because they broke themselves or had some sort of family ‘issue’ (granny’s birthday, cheap holiday and weddings have all been used as excuses) but it’s not difficult to find replacements from here.