I was a little shocked when I saw this just a few minutes ago:

You WILL need a security band to set up your tent. We will endeavor to get check-in set up as early as possible on Thursday so you can get set up, but we can't guarantee this before 6pm. Every effort will be made to make that earlier though.
From the above it seems that you have to have EAS to even get into the camping area and set up your tent. If you don't have EAS you won't be allowed to pitch until Friday since you won't be able to check-in until then!!! Here is some more info:

The key difference between Newbury and Stoneleigh is scale. At Newbury the events pretty much took over the entire site, as such there wasn't any problem with people turning up 'whenever' during the day, despite the event not officially opening to the public until 6pm.

At Stoneleigh, whilst the event is larger, the site is massive, there is the potential for other things to be going on. As such we're taking the precaution of protecting the campsite for your benefit. Unfortunately as a result this means we can't just let anyone in We're looking into all the options and I'm sure an appropriate solution will be found.
This is the thread with the details in. Luckily I have EAS already, but it is a shame that you have to have it just to set up tents on Thursday.