It depends on how quickly you made the post private!

For your subscribers who signed up for "Daily Updates" - as long as you "privatize" your post by midnight or so EST, you should be OK.  The post won't go out to your subscribers over our Daily Updates system.

For your subscribers who signed up for "Instant Updates", the timeframe is a bit more urgent.  As long as you make your post private by the end of that hour, you should be OK.  We generate Instant Update emails on the hour, so the only thing that matters is the status of your post on the hour.