It’s not unusual for Facebook to “move my furniture” once in a while. That happened recently with the “Schedule” button that used to appear with a little clock icon like this: 
Facebook is rolling out a change that eliminates the little clock in favor of a drop-down on the blue “Post” button. From that drop-down menu, you can now schedule your post to be published into the future, backdate the post to appear in the past, or save the post as a draft to be finalized later.
Here’s a quick video tutorial on how to use the new tool.