I have no experience of past gamejams so don't know how they work. I did talk to Simon about it yesterday on the Gamebook Zine Facebook page and he seemed very relaxed about it but I am thinking it might be fair if I submit my adventure early so that I will have had the same time working on it.
When I have a solid idea, I like to start writing as soon as possible and while I often hit first draft stage in a week or so I have always spent months if not years getting adventures to the point where I am happy with them, compared to the time we have.
Not being able to submit my adventure in the competition would not have been the end of the world. I have enjoyed the writing I have done on it so far and I have never won any creative writing competitions in the past. My previous success with solo adventures has always been where there has been no competition at all. They are after all something a lot of people would not even attempt to write.