I am not quite sure what is the relation between the grid and the RadDateTimePicker but I suppose that the last will be used for editing. If that is the case you can subscribe to the OnItemDataBound event and use it to first obtain a reference to the picker and then apply the desired changes.
Regarding the listed requirements it seems that we should handle only the case where the selected date is the current one. By checking whether the RadDateTimePicker.SelectedDate is the current date and binding the TimeView to a custom collection(as demonstrated here
) you should be able to make things work.
Note that it would be best to provide us with the markup and code-behind of the page so we could further examine the scenario. That would greatly facilitate us in providing a straight to the point solution.
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