I've begun a blog with 366 pre-built entries for the next year at http://pic.nslog.com/ .
I first tried setting the date and time to 00:00:00 (and GMT to 05:00:00). That didn't work and my entries weren't auto-published at midnight. Next I tried 00:01:00 (and 05:01:00). That doesn't work either.
Curiously, when you log in at, say, 9am, the post that should have been published at midnight will say it will be published in 9 hours. The math is backwards. The post that should go up at midnight that day properly says "in 15 hours."
I wrote more about this here:
http://nslog.com/2008/02/07/wordpress_time_bug_for_midnight_posts
I believe that the problem is the first 00, and I'll try 01:00:00 (and 06:00:00) soon, but there's still a bug.
P.S. WordPress 2.3.2 and 2.3.3 are affected by this bug. There's no choice for 2.3.3 in the popup.