This is here mostly for my benefit as I keep forgetting it, but this stuff is all over the internet.

Consuming and producing xmlschema dateTime formatted values is straightforward enough when you know the specification (see the link), briefly it is;

YYYY-MM-DDThh:mm:ss[.fff][zzzz]

The .NET class XmlConvert can be used to convert dateTime values between string and DateTime, using the ToString() and ToDateTime() methods.

   // convert from string to datetime
   var dt = XmlConvert.ToDateTime(dateString, XmlDateTimeSerializationMode.Utc);
   dt = XmlConvert.ToDateTime(dateString, XmlDateTimeSerializationMode.Unspecified);
   dt = XmlConvert.ToDateTime(dateString, XmlDateTimeSerializationMode.RoundtripKind);
   dt = XmlConvert.ToDateTime(dateString, XmlDateTimeSerializationMode.Local);

   // convert from datetime to string
   var dtStr = XmlConvert.ToString(dt, XmlDateTimeSerializationMode.Utc)
   dtStr = XmlConvert.ToString(dt, XmlDateTimeSerializationMode.Unspecified)
   dtStr = XmlConvert.ToString(dt, XmlDateTimeSerializationMode.RoundtripKind)
   dtStr = XmlConvert.ToString(dt, XmlDateTimeSerializationMode.Local)