1. limitation of the time that can be chosen (e.g. 8 AM to 5 PM)
2. set the interval of increasing and decreasing the Minutes part to 30 instead of 1

NO WORKAROUND

Resolution: 
In release Q2 2014 we are introducing logic that allow to set time range by MinValue and MaxValue properties of RadTimePicker. To set the interval of increasing and decreasing of the minute’s part you can use the MinutesStep property of the MaskDateTimeProvider. 

For example for RadTimePicker:
(this.radTimePicker1.TimePickerElement.MaskedEditBox.Provider as MaskDateTimeProvider).MinutesStep = 30;

For example for RadDateTimePicker:
RadMaskedEditBoxElement mask = (RadMaskedEditBoxElement)this.radDateTimePicker1.DateTimePickerElement.TextBoxElement;
MaskDateTimeProvider provider = mask.Provider as MaskDateTimeProvider;
provider.MinutesStep = 30;