If application engineers did their job correctly, they have nothing to update because you should store future events as a wall clock time + timezone, not an instant (ie something like `2026-09-01T09:00:00, America/Havana`, not `2026-09-01T09:00:00-05.00`).
Which means that flight booking systems are _probably_ fine (they're probably the domain that cares most about timezones and time changes so they've probably modelled it right), but many systems are not fine because it's such a common thing to get wrong.
Which means that flight booking systems are _probably_ fine (they're probably the domain that cares most about timezones and time changes so they've probably modelled it right), but many systems are not fine because it's such a common thing to get wrong.