Conversion API
RadTimeline allows you to convert a screen coordinates (a Point), to a DateTime value plotted on the timebar control. You can do that via the ConvertPointToDateTime method of RadTimeline. The method excepts an argument of type Point and it returns a DateTime object.
Example 1: Getting the DateTime under the mouse
private void UIElement_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
Point mousePosition = e.GetPosition(radTimeline);
DateTime date = radTimeline.ConvertPointToDateTime(mousePosition);
}