Key Takeaways
- Timezone scheduling on an Android SMS gateway is converting each recipient’s wall clock to UTC before scheduleAt — not trusting the modem’s clock app.
- The scheduled-SMS pillar owns the product walkthrough. This page is the TZ failure modes.
- POST /messages uses ISO-8601 UTC; live docs refuse scheduleAt beyond 38 days. Confirm in Developer Center.
- Quiet hours are policy in your adapter. The radio does not know local labor law.
- You bring the phone and operator credit. Platform pricing is devices plus send volume.
Store local, submit UTC
Product clock: scheduled SMS. Overview of fire-time radio failures: scheduled SMS overview. This in-depth page is why a “9am blast” lands at 3am for half the list.
We meter devices and volume. A TZ-correct queue still burns operator credit when it sends. Starter, Professional, and Business list Unlimited SMS as platform send volume; that is not unmetered carrier SMS.
IANA zones, not phone clocks
Keep Asia/Manila, America/New_York, Europe/London on the contact. Convert once at enqueue. Submit UTC on scheduleAt. Live fields: Developer Center. Zone database: IANA Time Zone Database.
“The handset’s clock is a display. The recipient’s IANA name is the contract.”
Failure catalog
| Symptom | Likely cause | Fix |
|---|---|---|
| Whole list at HQ lunch, locals asleep | One zone for every row | Per-recipient IANA; fallback explicit |
| Off by one hour in March/November | Fixed offset, no DST rules | Use a TZ library, not +5:30 hardcode for DST zones |
| Excel “9:00” as UTC | Naive datetime | RFC 3339 strings; see RFC 3339 |
| Phone Doze at fire time | TZ was right; radio was asleep | Last-seen + exemptions, not another offset |
| Rejected create | Horizon past live limit | Docs: scheduleAt refused beyond 38 days |
DST and split countries
Indonesia is three civil times without DST. The US is one country with many. Do not infer zone from country code alone. Quiet hours: STOP / auto-reply still apply when the local hour is legal to send.
OTP is not a reminder
Isolate login. OTP. Bulk lists: CSV.
Next steps
Canary two staff numbers in two IANA zones ten minutes apart. Confirm wall clocks. Plans: pricing. Operator credit stays yours.
Related product pages
Jump to the live product docs for this topic—not another long-form article.
- scheduled SMS campaignsSend later windows
- device and SMS volume pricingPlans and allowances
- Android SMS gateway product guideDefinition, product, and how to buy
- SMS API documentationLive endpoint reference
