I have created a C# class file by using a XSD-file as an input. One of my properties look like this:
private System.DateTime timeField;
[System.Xml.Serial
You could create a string property that does the translation to/from your timeField field and put the serialization attribute on that instead the the real DateTime property that the rest of the application uses.
Put [XmlIgnore] on the Time property.
Then add a new property:
[XmlElement(DataType="string",ElementName="Time")]
public String TimeString
{
get { return this.timeField.ToString("yyyy-MM-dd"); }
set { this.timeField = DateTime.ParseExact(value, "yyyy-MM-dd", CultureInfo.InvariantCulture); }
}