[TazeTSchnitzel]

> Except people want to be able to talk about times years in the future despite not knowing the number of leap seconds that may happen in the intervening time.

Doesn't the (TAI, leap second count) tuple solution work for this? Maybe I misunderstand the purpose, but you could use the leap second count to figure out how many seconds the TAI is off by.

But that doesn't matter, because date intervals shouldn't be represented with seconds anyway. Months and years have different lengths.

[TazeTSchnitzel]

…I forgot to mention this in my original comment, but real-world wall-clock time is in any case discontinuous due to daylight savings time and other timezone changes. This means that it's not only months and years that change in length, but days and weeks too.

[wereHamster]

You can not represent "Next Monday at 12:00" with a tuple (TAI, leap second count), because you don't know how many leap seconds there should be. Or maybe you know for next Monday, but you definitely don't know for the Monday in a year, as leap seconds are only announced ~6 months in advance.

[beering]

I think you cannot represent "Monday in a year at 12:00" with a simple integer either, right? For example, the king of the country may decide to cancel DST for the year. Either way you would have to store it as a calendar event and figure out the exact time once you're closer.

[dom0]

You should store that similar to this:

    begin = (today, 12:00) (eg. 2017-01-01T12:00:00)
    repeat = RRULE:FREQ=WEEKLY;COUNT=1;BYDAY=MO

Note that "begin" is usually something software figures out itself.