You could use a three-pronged approach:
1. Use cron (on OS X/Linux) or something similar to execute the publishing on a schedule.
2. Keep your blog locally in a Dropbox folder.
3. Use an iOS app (e.g., Droptext) that syncs via Dropbox to edit posts.
There is a little marginal work to do, e.g., writing in a _drafts folder and moving to the _posts folder (which the cron job targets). The Dropbox app for iOS will suffice.
This will work, and even smoothly once it's set up. It may not be the elegant approach you're looking for, though.
Cheers,
Daniel