Seems I was a little too quick on the trigger – future posts will be shown but cannot be accessed when not logged in. When trying to access them without being logged in, I get a 404 error. Now using the “Future is now” (http://wordpress.org/plugins/the-future-is-now/) plugin, which seems to work.
Here is a solution to make the plugin version 1.3 work with WP 3.9.
After a little research it seemed to me the cleanest way to solve the problem.
I pasted just the relevant lines, where you have to change the calls to “$wpdb->prepare”. Correct me if I’m wrong.
http://pastebin.com/wiZCZYyg
Cheers, Jakob