I really really dislike this interface, sorry.
`struct tm` contains so many members that don't belong in there.
The hardware RTC will probably provide year, month, day, hour, minute, second.
But `struct tm` also contains the day of week (that starts with Sunday for no apparent reason), the day in the year, and whether daylight saving time is active. Except for maybe `chronos` none of the latter information are useful.