@Override
    public void setTimer(Timer timer) {
        this.timer = timer;

        if (timer != null) {
            timer.reset();
        }

        if (renderManager != null) {
            renderManager.setTimer(timer);
        }
    }
Sets the Timer implementation that will be used for calculating
frame times.  By default, Application will use the Timer as returned
by the current JmeContext implementation.
jme3-core/src/main/java/com/jme3/app/LegacyApplication.java