And the answer appears to be: yes I can, and they get sorted correctly for public display, but on the dashboard they appear in the order created.
Edit (April 8th 2011): This post is getting a lot of views via Google, from people who’ve searched for things like “backdate posts tumblr”.
You’re going to be penalized by posting content that isn’t yours originally.
The reasoning is that, when Google sees the two posts, it will compare their dates and give authority to the earlier post. Many black hat webmasters don’t pay a lot of attention to the content they’re stealing, nor the historical perspective driving that content.
The issue is that a lot of times the original post may be commenting on current events.
You can then edit the post date to maintain consistency from one site to another.
Of course, these days a site migration generally includes post dates, unless you’re doing a drastic move from one blogging platform to another and your only backup doesn’t work with the new software.
Word Press, as one of the most popular blogging platforms in the world, offers the ability for users to change the date on their posts, both before and after they have been published. You can set a post to appear in the future, scheduling your content drops. What about changing the date on a current post to make it look older? How can it be used, legitimately and illegitimately, and what is Google’s opinion on the practice?