I'm having some trouble with adding times in excel. I'm completing a time study for my company and we want to track how long our entire process is for our the customers. Below is a sample of my spreadsheet:

Customer Check-in Time Check-in Date Total time for Customer Customer Check-Out Time
8:50 1/11/2014 9:25 18:15
14:07 1/12/2014 27:00 ???

I use a formula to add the check-in time with the total time to calculate the check-out time, as you can see in the first row. My question involves the second row. How do I add the check-in time with the total time, since the customer was here for more than 24 hours? When I try to create a pivot table with all the data, I'm given the 1/1/1900 date. I figure this is because the total time is more than 24 hours. Any suggestions on how I can add these times? I was thinking about adding a check-out date column for these types of scenarios, but not sure how to do that.

Thanks for your help!