There's going to be 2350 riders there - they're intending to send the majority of timing chips and numbers out in advance by post so no sign on will be nescessary. That means its first come first served on the line.
When you turn up you'll be moved into pens and started in groups of 100. rather than by what number you have.
This means that if you want to ride with your mates all you have to do is turn up at the same time and you'll be in the same group.
It also means that you can loiter at the start and look at the quality of riders lining up and decide whether a) you fancy giving a bunch of nodders a kicking, b) you think you can mix it with the ultra-fast Cwmcarn paragon guys or c) what the hell, you're going to get roasted whatever happens so you may as well start early and get it over with asap