I don't know about that, they've been more than generous so far so I wouldn't want to push it really. A month is a long time though, you can start for the first week just trading with 50p bets if you wanted until you get the hang of it. There are dozens of horse races every day, even if you just traded on half a dozen you'd get a good feel for it.
If you want to get an idea of how it works you could have a look at the videos on the site:
Yes as Andy says I am just finalizing things at the moment and hope to have the challenge live for the week running up to July (24th June onwards) so people can register at Betfair and I can confirm those registrations. That's the plan anyway, will see how it goes.