I'm investigating some weird stuff going on with WLW and BlogEngine 1.3. Posts aren't being published, lots of null reference exceptions... I'll post about it once its nailed down.
Update: Stay away from the post date in LiveWriter and all is well. If you run BlogEngine 1.3 and LiveWriter and you want to delay post, just save your post in drafts and send it manually when you want it to appear. Its kind of a pain in the ass but that's the way it works for now.