I had tried that feature before giving up on Outlook and switching to Thunderbird. For me, it acted more like a "draft". The message would sit in the Outbox without being sent prior to the scheduled date. However, it would still be sitting there after the scheduled date. I would have to remove the schedule setting to get it to send. That's not the way it's supposed to work, of course. Have you ever encountered this problem? Could be that it was just one more of the things that stopped working for me in Outlook; the program (2007 version), just seemed to self-destruct. All of the Microsoft diagnostics said there was nothing wrong with anything. Even a re-install of Outlook without updates (original condition when it used to work), wouldn't work any more with Windows 7 as currently updated.
Yeah, I kind of figured it was corruption (Outlook couldn't write to the PST file without corrupting it, literally). There were multiple features that didn't work properly and it kept crashing. I finally gave up on Outlook and resolved it by changing to another program. I showed Microsoft! Bet they're sorry now.