Appointment series were the example that I gave earlier where you will have to use some more complex data structure than a simple date time value and correspond

Appointment series were the example that I gave earlier where you will have to use some more complex data structure than a simple date time value and corresponding logic to get it right. You can obviously not find the correct instants for a weekly meeting by repeatedly adding 168 hours to the instant of the first appointment. But this thread started from specifying a date and time of day in some place far into the future and I do not think an indefinite appointment series qualifies for this. Your scheduling application would most likely store something like every Tuesday and 13:00 and figure out the actual instants as needed, for example to show a reminder. And as it received updates about changed daylight saving time rules, it would recalculated the instants.