When you export your Microsoft Office PivotTable list to Microsoft Excel, 12:00:00 AM
is displayed in the PivotTable where you expect a date to be.
This problem occurs when your PivotTable list contains dates earlier than January 1, 1900. Excel does not support date values earlier than January 1, 1900.
Excel converts dates earlier than January 1, 1900 to a value of zero. The value of 12:00:00 AM that you see is the result of the default formatting that Excel applies to the number.