I'm curious how disruptive this would be from a database perspective ? For eg, All the flight bookings to/from Cuba needs to be updated because it would have originally accounted for DST.

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.

well https://www.iana.org/time-zones/releases/2026f has the right info. If they stored everything in the DB as UTC... this is like a DNS change. Downstream partners need to have a TTL on it.