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Comment by bl4ckneon | Hacker News Reader

Would like to understand too. On a new android 10 phone it was 1.7 seconds. Not that large, but in computer/processing time it is pretty large.

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Phones need to work with the cellular network, so they sync their time with the cellular tower using a GSM protocol (NITZ) and not NTP.

Your phone's settings should have a way to sync with the cellular network (for example, if you set a manual time and then choose set time automatically).

Cell towers (edit: in the USA) are usually within a second of time.gov, so your offset should hopefully be under a second after you sync with the cellular network.

While cellular towers uniformly use a GPS time source for TDMA reasons (which is exactly synchronized to the Naval time minus a known offset), they are surprisingly inconsistent about how time information is delivered to handsets. CDMA requires that towers rebroadcast exactly the GPS time, but GSM generally does not. As a result, GSM handsets may have less accurate time sync depending on how the time service is actually provided.

It's somewhat common for CDMA cellular equipment to be used as a stratum-1 time source in lieu of GPS, since CDMA is easier to receive inside buildings. But GSM is unsuitable for this purpose, and since the long-term prognosis for CDMA seems perhaps less than optimistic, some operators may be forced to run a GPA antenna to the roof.

My iPhone is showing 0.024s for an extra data point.

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