UE.5.3) Cycles64 gives inaccurate result

Development Programming & Scripting C++
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1 
uint32 FTestThread::Run()
{
	uint64 tLastStampedCycle = FPlatformTime::Cycles64()

	while(bStop)
	{
		uint64 tCurrentTimeCycle = FPlatformTime::Cycles64();
		const double DeltaTime = FPlatformTime::ToMilliseconds64(tCurrentTimeCycle - tLastStampedCycle ) * 1000.0;
		tLastStampedCycle = tCurrentTimeCycle;

		FPlatformProcess::Sleep(0.003f);
	}
}

This is async-task operation (used FRunnable).

This code keeps giving me inaccurate Deltatime.
The actual time differs by more than 10 seconds.
I would like to know what the problem is