Documentation for postDelayed:
> Causes the Runnable r to be added to the message queue, to be run
> after the specified amount of time elapses.
> The runnable will be run on the thread to which this handler
> is attached.
> <b>The time-base is {@link android.os.SystemClock#uptimeMillis}.</b>
> Time spent in deep sleep will add an additional delay to execution.
TL;DR: if the CPU is in deep sleep, the postDelayed runnable won't be executed.
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