If I understand correctly your requirement, you are trying to stop the user to enter some digits in the RadDateTimePicker. You can achieve this via the RadDateTimePicker.DateTimePickerElement.TextBoxElement.KeyPress event:
If it is not the exact requirement, please specify more details about the expected behavior. Thus, we would be able to investigate the precise case and suggest an appropriate solution.
I hope this information helps. Should you have further questions, I would be glad to help.
Regards,
Desislava
Telerik
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