The only issue I would have with a timed event, is that anyone who has track insurance (either standalone, or with their road policy) will have it negated by the 'competitive' element of this event.
I'm also not sure it's such a good idea for the organiser to advocate pushing yourself and the car to/over the limit for a bit of fun. I'd prefer to pay £50-£100 more and have a full day event that I can take at my own pace.
If you don't have insurance, then it is not an issue.