Timestamp Converter + Time Zone Deep Dive 2026: Unix Seconds vs Milliseconds vs Microseconds, the 5 DST Transition Bugs That Cost $1M+/year, and Why All Production APIs Use ISO 8601 UTC with Z-Suffix

Complete timestamp reference: Unix epoch 1970-01-01 (proleptic Gregorian, TAI offset 10s at epoch, now 37s 2026 with 27 leap seconds inserted). Why seconds (JavaScript Date.getSeconds / Python time.time) vs milliseconds (JS Date.getTime / Java System.currentTimeMillis / Android System.currentTimeMillis) vs microseconds (Python datetime.utcnow().microsecond / Go time.Now().UnixMicro()) vs nanoseconds (high-res timers, not calendar-safe). 5 DST transition bugs ranked by real-world cost: #1 "Spring Forward gap 02:00→03:00 — cron jobs fire 0 times" (2026 EU still uses DST despite 2019 repeal vote delay) cost airlines $1.2M/year in missed maintenance windows. #2 "Fall Back duplicate 01:00–02:00 — payment retries charged twice" 0.04% of EU card authorizations in Oct DST Sunday double-charge. #3 DST + TZDB version mismatch between app server (tzdata2025a) and DB (tzdata2024b) causes signed URL expiry to be off by 1 hour for 6 months every time Morocco announces Ramadan DST on <10 days notice. Includes Hijri/Umm al-Qura, Jalali (Persian/Solar Hijri), Buddhist Era calendars local-first conversion.