Audience-
SharePoint site admin and news post builder
Go to the news post (Make sure your in edit mode). Click "Page Details" and on the right side section look for the scheduling toggle and turn it on.

select the date and time,

Click "schedule" or go back to editing and "Save As draft".

Important: If you need to edit a scheduled page to update the content or change the scheduled time and date, you must schedule the page again by selecting Schedule. If you don't do this, the page will not publish at any time. You can also edit a page and remove scheduling. In this case, you can publish the page immediately by selecting either Publish, Post news, Republish or Update news.
Working with News post approvals
Scheduling can work in conjunction with page approvals. If page approval is set up for a site, and an author schedules a page or news post for publish, the page must first be approved.
- After the page is approved, the page is published at the scheduled date and time.
- If the page is approved at a time later than the scheduled time, it publishes immediately upon approval.
- If the page is not approved, it is not published.