You have to differentiate between calendrical and chronological calculations.
So to walk through your requested example…
You store a TAI time stamp of when you originally chose a specific date/time and then you store either a chronological time stamp (the TAI value) or a calendrical timestamp which is a struct/dict/etc storing the desired year month day, time and timezone and notionally the calendar system unless you want to assume the Gregorian calendar and risk confusion with Julian calendar dates which are still in use for astronomical record keeping. With these two values you can calculate what to change in the struct to account for any time change, a day not being fixed as a number of seconds allows accurate calendar calculations. You increase the day value and make sure you don’t have to “carry” a month in the months column.
Yes this is more calculations when modifying a value compared to just adding a bunch of seconds but that’s the issue at the heart of this problem, calendars and chronological elapsed seconds are fundamentally different and we computer programmers tried to take a big shortcut by using a single seconds value for both… and thus… here we are with the present state of affairs.
So to walk through your requested example…
You store a TAI time stamp of when you originally chose a specific date/time and then you store either a chronological time stamp (the TAI value) or a calendrical timestamp which is a struct/dict/etc storing the desired year month day, time and timezone and notionally the calendar system unless you want to assume the Gregorian calendar and risk confusion with Julian calendar dates which are still in use for astronomical record keeping. With these two values you can calculate what to change in the struct to account for any time change, a day not being fixed as a number of seconds allows accurate calendar calculations. You increase the day value and make sure you don’t have to “carry” a month in the months column.
Yes this is more calculations when modifying a value compared to just adding a bunch of seconds but that’s the issue at the heart of this problem, calendars and chronological elapsed seconds are fundamentally different and we computer programmers tried to take a big shortcut by using a single seconds value for both… and thus… here we are with the present state of affairs.