That’s how the framework works: things appears in streams when you create them and I don’t think I can change this, unless you create it hidden but that wouldn’t make sense as it would be visible to moderators only or use the future publish to it but then someone will again lose the date. Update the date will have no effect here.
It sends a notification to when it’s ready (author set it as ready), so people who follows the category will be aware in the proper time. Also, if you use the option create a topic, it will create only after the author set it as ready.
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EDIT: Just remember one thing. I can probably remove it from the search index right after create it, which remove it from streams, and add it when the author clicks in the Set Ready. The downside here is that will “disappear” from everywhere, including author profile so he would need to browse to the categories to view it. And it will be visible to everyone in the category. So not sure it will worth the job.