Sum Hour in Text Values

Hi all,
I have the following timesheet sharepoint list:
Start period 1: 08:00
End period 1: 12:00
Start period 2: 14:00
End Period 2: 10:00

All values are recorded in text, so in Total column I'm use this formula:
=TEXT([Start period 1]-[End period 1]+[End Period 2]-[Start period 2];"HH:MM")

In SharePoint I can see total values, but is returned error in SSRS.

How I can sum hour in text values?

Douglas Filipe http://douglasfilipe.wordpress.com