On the RadDateTimePicker with TabIndex set...only the CalendarPopupButton inherits TabIndex from parent picker while TimePopupButton does not.
So user will tab to the DateTimeTextbox and then tab to Calendar <a> tag...then tab order will skip over the TimeButton.
I have this workaround.
$(function () { setTimeout(function () { var fromToDatePicker = $find("<%=RadDatePickerFromTo.ClientID%>"); var fromToTimeControl = fromToDatePicker.get_timePopupButton(); fromToTimeControl.tabIndex = fromToDatePicker.get_textBox().tabIndex;