I updated the sources for AvalonControlsLibrary v2 so that to support MinDate and MaxDate in the DatePicker.
Also added support for MinTime and MaxTime in TimePicker.
And while I was at it I also refactored the DateTimePicker to support these 2 properties.
The properties are DependencyProperties so you can easily databind to and do what every you like with them….
C# Disciples 
I need this