Implement two-digit year parsing referred as €œThe 2029 Rule€ in the control like the parsing in Excel.
Examples:
In Excel: typing 1/1/70 returns 1/1/1970
In RadDatePicker: typing 1/1/70 returns 1/1/2070
For more information use the description at this link

Used to clear the Input field and set the SelectedValue to null, include dependency properties like ClearButtonVisibility and ClearButtonContent.

There should be a property like StringFormat, which can be set to something like "dd.MM". This is really common way across all wpf controls, and it's frustrating that currently it can be done only using code-behind. It's not MVVM friendly at all.

Currenly if you update the Value it will update the text as well preventing further digits to be entered in a meaningful way.

Change the time picker to a way that you can 'zoom' in on the time. In the same way as the decade>year>month zoom of the date part.

To be able to select times till minute or second precision

one of my users has requested the ability to have the daytime picker pop-up closed when you double-click on the time.  could this please be added into a future release. I have written some code to do it in the meantime in ClockItem.cs:

// Stefan: start
        protected override void OnMouseDoubleClick(MouseButtonEventArgs e)
        {
            base.OnMouseDoubleClick(e);
            var dateTimePicker = this.ParentOfType<RadDateTimePicker>();
            if (dateTimePicker != null && dateTimePicker.InputBox != null)
            {
                dateTimePicker.IsDropDownOpen = false; // close it.
            }
        }
        // Stefan: end

Research and implement if possible to choose seconds TimeInterval.

A client could change the TimeZoneInfo in the DateTimePicker control so it will shows the DateTime information different from the current machine.