Starting in Android 12, Android can optionally use an external source of time to suggest Unix epoch times to the Time Detector service. This isn't enabled by default in AOSP.
The external time origin lets you provide completely custom time suggestions
to Android. After receiving suggestions from the external time origin, the
time_detector service determines whether to update the system clock based on
the configured automatic time prioritization rules.
Implementation
To support external time detection, you must implement a component that submits
external time suggestions to the time_detector service through a system API
call.
To configure the external origin, use the core/res/res/values/config.xml
system server configuration file. Add the value external to
config_autoTimeSourcesPriority.
The following example tells Android to give external time suggestions the
highest priority when setting the system clock. If there is no valid external
time suggestion available then the next origin, gnss in this case, is used:
<string-array name="config_autoTimeSourcesPriority">
<item>external</item>
<item>gnss</item>
</string-array>
To provide the system with an external time suggestion, use the
suggestExternalTime method in TimeManager. If the external origin is
configured using config_autoTimeSourcesPriority in the configuration file and
no higher priority time suggestions are available, Android uses the timestamp
passed to this method to set the current Unix epoch time.