Brad,
First of all, is Project 2013 updated with the latest update? If not, or you're not sure, run Windows Update. Project 2013 should be 15.0.4885.1000 (December 2016 update).
What is the base calendar that you apply the exception to? Hopefully it is either the built-in "24 hours" calendar or a custom calendar you created for a 7 day workweek. Try the following. In the Change Working Time window, select the two days
as shown.

Then create the exception. When you click on the Start field, Project will automatically set the Start and Finish for the selected days

Hope this helps.
John