Dates in XML forms can be formatted in various ways, for display purposes, but the XML source stores the date in XML format. Save the XML and open it in Notepad if you wish to see what that format is exacty.
Sometimes, depending on the source of the data, the formats differ. I've seen
2013-12-30T01:30:30
and
2013-12-30 01:30:30
Some cleanup in the form might be required before the dates are pushed out to SharePoint, SQL, etc.