const keyDown$ = Observable.fromEvent(window, 'keydown');
const keyUp$ = Observable.fromEvent(window, 'keyUp');

keyDown$
    .filter(/logic to get the right arrow keycode/)
    .subscribe(downArrow => moveElementToTheRight())

keyDown$
    .filter(/logic to get the right arrow keycode/)
    .sample.pipe(interval(200))
    .subscribe(downArrow => moveElementToTheRight())

keyDown$
    .filter(/logic to get the right arrow keycode/)
    .map((value, index) =>
        if index < 10 return value every 500ms
        if index between 10 and 20 return value every 200ms
        /etc/