QTimer is slowing down

[Lodhart]

At first I know that Windows is not realtime system, so I really do not expect that QTimer will have some bigger accuracy. But I can see that my QTimer is slowing down from 200ms timoeout to 500ms timeout in ~7minutes.
I am using debug output and timing stamps so I really can confirm that QTimer is slowing down. I am using like this:

void timeoutFnc() {
  stopTimer();
  /* doing something (it can takes 1s) */
  startTimer(200);
}

void timeoutFnc() {
  stopTimer();
  /* doing something (it can takes 1s) */
  startTimer(200);
}

To copy to clipboard, switch view to plain text mode 

So I need from each run 200ms distance. My idea is that maybe it is not good to stop and start QTimer so many times. But I need this behaviour.