Welcome to the Q&A Forum

Do a Google Search for a block of text on the page to see if there's other pages in the SERP that have the exact same text. Google may be crawling some other page that's too similar and giving you a duplication penalty. I've seen domains with their authority in the sixties not showing up and getting beaten by domains in the thirties because of it.

What are you really scheduling if it's remaining online until the date when you want to "post" it? What you're asking for essentially is for an ability to schedule a change in an existing page's post date for some time in the future. This isn't really going to help you with SEO, and might actually hurt you in terms of duplicate content. It certainly isn't practical if you're putting dates in the permalinks.