Storage & interchange
Persisting and exchanging time across databases, formats, and the wire.
PostgreSQL
timestamptz stores an instant; timestamp stores civil wall time with no zone.
MySQL / SQLite
DATETIME vs TIMESTAMP in MySQL; and SQLite has no real date type at all.
MongoDB
BSON Date is UTC milliseconds since the epoch — no zone fidelity.
JSON
JSON has no date type — pick a strict string format and document it.
YAML
YAML does have a timestamp type — and it will coerce your strings when you least expect it.