When StartTime = EndTime all hours are visable (12 am - 11pm)
Workaround:
Select EndTime in one hour interval from StartTime (10:00 - >10:01). In this situation only 10:00 will be visible

Create property that allows to open the dropdown on focus or change the implementation of the control so this can be achieved by code.

RadDateTimePicker ControlTemplate: PopupPlacementTarget in RadDropDownButton is not respected when FlowDirection of RadDateTimePicker is RTL. PopupWrapper issue.

When set DateSelectionMode="Month" and SelectionMode="CenturyView", the calendar in the dropdown starts from YearView instead of CenturyView

RadDateTimePicker cannot parse datetime string when Windows date format is set to "Chinese (Traditional, Taiwan)".

Forbid typing a date earlier or later than a date if SelectableDateStart/SelectableDateEnd are set. Can be achieved by custom parsing.

Available in the 2016 Q1 Release: Implemented IsInputRestrictedToSelectableDates property in order to allow only selecting dates by input in the selectable range (when SelectableDateStart/SelectableDateEnd/BlackoutDates are used).