When posting stories in channels which have a publishing schedule enabled, those stories don't get published immediately. Instead, you submit the story to the channel. Submitting your story puts it in the channel's publishing queue. It, along with all the other stories submitted to that channel's queue, will be published in the channel's next edition. When that edition is published is determined by the channel's publishing schedule.

Submit your story

When you're writing your story in the story editor, if the channel you've selected for the story has a publishing schedule, you will see a submit button instead of a publish button. When your story draft is ready to go, just click the submit button in order to put it in the channel's publishing queue. At that point, your story will be in a submitted state, and you cannot edit it.

Unsubmit your story

If you want to edit your submitted story, you can unsubmit it. Doing so will turn it back into a draft, and you will be free to edit it.