As @inertia pointed out there is no way to do it directly on Steemit.com at the moment. But it's one of the features and advantages of using Streemian.

Visit this link https://streemian.com/ and register.

The verification process is a little tedious, but not too hard to do. Once you have your account on Steem connected to Streemian, you can have full access to all its features.

That being said, precisely on the subject of this post. Streemian can schedule them exactly as you want, but their editor is quite basic. So what I would recommend anyone thinking about using it for this purpose, would be to start the post on Steemit... double and triple check for errors and what not.... and then copy past the code itself onto Streemain to schedule it. That way you know more accurately how it's going to look on Steemit.

If you need helping setting any of this up, I'm here as always.