Does anyone know how much data is used for iOS to keep time synced with the official time?


macrumors 6502
Original poster
Apr 30, 2014
I'm sure it's very little data, but still would be nice to see an accurate number (I don't want to know for data usage, I want to know for curiosity, and maybe how often it checks to see it's synced.)

Maybe some nerd had graphed the packet data on the phone to see when and how much data the clock sync was using?

Bonus question: does anyone know what Apple is syncing their time from? like which clock it syncs from if there's an official atomic world clock or something that is accurate to the 0.0000000000001 seconds or something real scientific.

It would be neat to see a video if it exists of lets say, 10 people with iphones on a table and recording in 240 fps to see how in sync they are were.

k thanks


Staff member
Jul 1, 2014
Not a real answer, but, something to start with.

Macs use Apple's own time servers (in US,

The US atomic clocks time services:

Although network conditions vary widely, our tests suggest that most users should realize a timing accuracy of 50 milliseconds (0.050 seconds) or better when using this (or any other) NIST server.
Big thing, though, if a cellular device, neither are used (directly). Device is getting time information from the cell towers themselves, so no data involved. And if I recall correctly, cell networks have similar accuracy as above. Cell tower because of billing (think back in the days of night and weekend calling packages), e911, crossing over timezones (and with GPS disabled on device), believe handoff between towers is involved, and so on. Wrinkle in all this as well: seem to recall GSM and CDMA have their own time requirements.

From what I recall, an NTP (aka the time daemon) sync request is like 2KB worth of data usage.

Guessing no two phones would be identically in sync due to when/where pinging for time, when device booted and how fast vs other, what "phase" internal circuit clock is vs other devices (ie. Not human time but the GHz part of of time when reading about CPU speeds etc), updating clock image(s) require OS resources/calls/semaphoring, so will be some level of lag there.
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