I've got an idea for a story, or series of stories, based around the ideas of the Christi stories by adventerer2003. I don't really want to do them unless he's okay with them, even though his characters don't appear in the ideas I have. I've PM'd a few times now, but with no response as it looks like he hasn't been on over a month. Should I wait for a response for a little while longer, or just go ahead? How long should we hold off before using someone else's concept?