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

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

        if (renderManager != null) {
            renderManager.setTimer(timer);
        }
    }
Sets the {@link Timer} implementation that will be used for calculating
frame times.<br><br>
By default, Application will use the Timer as returned by the current {@link JmeContext} implementation.
@param timer the timer to use.
jme3-vr/src/main/java/com/jme3/app/VRApplication.java