Date, Time, and Timezones in Business Apps — From DateTime Pitfalls to the UTC-Storage Principle and Test Design (archived 2026-07-27)

Timestamps drift by nine hours after a server migration; only the overseas office's dates roll back to the previous day — we trace date/time incidents back to DateTime's Kind property and its implicit conversions. This article covers when to use DateTimeOffset instead, the principle of storing UTC and ISO 8601, TimeZoneInfo and daylight saving time, the boundary with SQL Server/SQLite, and test design with TimeProvider, all from a hands-on engineering perspective. Archived version of https://comcomponent.com/en/blog/business-app-datetime-timezone-guide/, as published on 2026-07-27. The live article is maintained and may change after this date. First published 2026-07-03.