FWIW, I suspect the issue was that the post_modified and post_modified_gmt still reflected the old timezone. I worked around the issue by doing the following:
1) Quick-edit post, change the post date to 10:01. Click update
2) Quick-edit again, set back to 10:00, click update.
3) Repeat for every scheduled post.
I suggest a check somewhere in WP to look for mismatched timezones to prevent this.
