Actually, your mini-courses are released the moment you start creating them; anyone with the share link can view the content. Changes made on your mini-course are saved instantly. When you finish editing your mini-course, you don't need to publish it as it is live already.
Suppose that you want your mini-course to be hidden while you work on it and make changes. There are two solutions available for this case:
You can prevent unauthorized viewing by adding a password wall at the beginning. When you feel that your mini-course is ready, you can simply delete the password wall from the mini-course and continue using the same mini-course share link with your learners. Here's further information on password protection card.
You can move your mini-course to another collection while you work on it and when you're done making changes, move it back to the collection it belongs. Here's how to move mini-courses through collections.