There is no property indicating the next DateTime that user is going to,

for example, we are in November/2022 and the end user click on "<" back button,

the event return the current date.

RadCalendar1_OnHeaderCellRender

the  var nMes = cal.FocusedDate.Month; to return the current month.

When handling the SelectionChanged event on a Calendar with EnableMultiSelect="true", there is no way to determine the new selected date(s). The SelectedDatesEventArgs exposes the entire range of selected dates, but it does not tell which of those dates were previously selected. Add a property to the event args that would expose this.

OR

Add an attribute to the RadCalendar when EnableMultiSelect="true" to "DeselectWhenSelectingNewDates." If this is set to true, any date selection on the calendar would deselect any previously selected dates.

We have just got issue with WCAG compatibility when applying for WCAG certification.
 The problem is that RadCalendar used for RadDatePicker has a strange behaviour when tabbing. We can't get focus to buttons (<<,<, >, >>)  that are in the header of the Calendar popup. We can successively navigate contemt of the Callendar -days of the month both with Tab and arrow keys (with EnableKeyboardNavigation="true"
 ) , but not to header buttons.
 We found nearly the same problem on Telerik demo: http://demos.telerik.com/aspnet-ajax/calendar/examples/functionality/keyboardnavigation/defaultcs.aspx

 Please look that Calendar at the top of the page does not allow select its header buttons. But the one in popup inside RadDatePicker can tab to its header buttons. 
 (however in strange way order is: days navigation inside Calendar1 by arrows, Tab- RadCalendar1, Tab- header of Callendar1 first button: <<)

If it is possible, I'd like to be able to select the hour and minute individually from the same popup/dropdown.   
Currently, if you set the interval to anything less than 15 mins the list becomes far too big, imo, and forcing the list to scroll isn't always the most usable way to do things, especially if that list is particularly large (intervals of 5 mins or lower).

It would be really handy if the user could somehow choose the hour and minute separately before the popup/dropdown closes. This would minimise space used because you wouldn't need every instance of each hour/minute combination. You'd just need the hours displayed, and the minutes displayed.