No need to post works in progress, just post it whenever it's done. No need to feel forced to post either. With timelines, as I've discovered, posting deadlines become superfluous. However, I'm not going to break the seven day thing myself, so I'm always going to advance the story every seven days. The longer you wait, the more catching up you'll have to do, that's all—which might be daunting if you skip out on posting for too long.