Yes, when you are scheduling a post, you are presented with a couple of opportunities to save it as a draft.

Depending on what stage you're on when scheduling the post, you'll be presented with either of the below options at the bottom of the Schedule A Post window.

(step 1)

(steps 2 and on)

After you've saved a post as a draft, you can retrieve it by clicking on the Publishing drop down then Post Drafts.

Then locate the post you'd like to edit/publish, and click Continue Editing to bring the Schedule A Post window back up for that post.