I sent this to support, but in case anyone reads this here and can confirm I'm not crazy:
Twice today I have had a prepublished post (set the time-stamp to the future) not show up on the main blog after the publish time. The second time I went and viewed it (via the Manage Pages dashboard) and the next post/previous post were listed on the top (next post had just been posted live), so it was clearly past the time I had set with the time-stamp. Both times I was able to get them to show up on the main blog page by hitting the publish button on the edit post page (and it retained the time-stamp from the first prepublishing). I've never had problems before prebublishing before, they always show up at the time I've selected.