It looks like the February 2016 updates for Outlook 2013 changed the behavior of appointments that span two days. When this change was implemented in Outlook 2010 it created an outcry among users, leading Microsoft to remove it as of the upcoming March 2016 updates. It looks like Microsoft didn't get it removed from the Outlook 2013 update.
The updates this month address the following issues:
When you click the To, Cc, or Bcc button to show the address book, Outlook might crash.
When you forward or reply an HTML email message that has some images, one or more attachments or inline images may be lost.
When you send multiple items at the same time, the send isn't blocked for the items beyond the first send under certain circumstances.
The Communicator client crashes with an olmapi32.dll error when it integrates with Outlook. Communicator 2007, Communicator 2007 R2 and Lync 2010 are affected.
When you forward a message that's created based on a custom form, Outlook may crash when you click send or close the original message.
To install this month's update, check for Updates in any Office product. For
more information, see February 9, 2016, update for Outlook 2013 (KB3114729)