[ewi_]

Very good point, which is a reminder that you have different "types" of dates that you may want to store.

Went storing the time at which an event happened (e.g. for a system log) then a UTC or UNIX time works, and it will be transformed at display time depending on the user's timezone.

When storing a future time at which to do something, it should be stored with its target timezone so you can always make sure it happens at the right moment. For this iso datetime representation makes a lot of sense.