> how daylight savings works in Ada.Calendar
Given ARM 9.6(23) "The time base associated with the type Time of
package Calendar is implementation defined. ..." and (24) "... as
appropriate to an implementation defined timezone;", it seems to me you
can assume nothing about daylight savings and Ada.Calendar.  You'll have
to go to the particular OS or something.  In Claw.Time (MS Windows) we
ask the OS about daylight savings stuff to convert to/from UTC (aka
GMT).  Java presumably does the same.  Similarly for Unixes.