Click on File to access the backstage.
Choose Automatic Replies (Out of Office).
Check Only send during this time rage:.
Set the start and end date and time.
You can also to choose to send the same or a different message to those outside of your organization.
Click on Outside My Organization.
Choose to send the Auto-reply to those only in your contacts or to anyone outside of the organization.
Click on the white arrow in the upper right-hand corner to return to the inbox.