Thank you for writing.
There is an issue with the behavior of RadDateTimePicker indeed. If the culture does not use the AM/PM time format, the user cannot set the hours to be greater than 12. I have logged this issue to our Public Issue Tracker under ID 11881. To vote for it and subscribe for its status updates, follow this link: http://www.telerik.com/support/pits.aspx#/public/winforms/11881
. Thank you for reporting this issue and please excuse us for the caused inconvenience. Your Telerik points have been updated.
We will do our best to address the issue for our upcoming Service Pack, scheduled for the end of the month.
I hope this helps. Let me know if you have further questions on the issue.
All the best,
the Telerik team