InfoPath Dev

I have a PDF Form that creates a xml file when completely filled and submitted and they are saved within a sharepoint form library.  I would like to utilize the InfoPath template to calculate the date and time to utilize the Gnatt view for this library.  The problem is Sharepoint views all the xml data as strings and the calculated columns in sharepoint are not usable for Gnatt view.

The field names are DepartDateRow2, DepartDateRow6, DepartTimeRow2 and DepartTimeRow6 for the combination of dates and time.  The format of the date is MM/DD/YYYY and time is HHMM.  I would like to combine DepartDateRow2 with DepartTimeRow2 to create the start position and combine DepartDateRow6 with DepartTimeRow6 to create the finish position for the Gnatt view.

How do I create this value with in the InfoPath template so when I import a XML file the data is automatically populated?

<DepartureDateRow2>08/17/2013</DepartureDateRow2> 

<DepartureDateRow6>08/18/2013</DepartureDateRow6>

You need to make sure it's in the correct date format for XML - that's 2013-08-17.