Hi Luc,
Thank you for writing.
The type of RadDateTimePicker's Value property is DateTime. You should parse manually your XML date to the .NET type DateTime and pass the result to the Value property.
I would like to clarify that RadDateTimePicker does not support milliseconds editing. I would suggest that you parse the value to seconds, without milliseconds.
Let me know if you have additional questions.
Regards,
Peter
the Telerik team