The event script is running on the same thread as the GUI. So when you call time.sleep(), it’s actually preventing the screen from being repainted.
What I would recommend is instead using a timer component with a property change event handler on it. Then, every time the timers property changes, it moves the proper component a certain number of pixels using system.gui.moveComponent(). This continues until the component has been gradually moved to the new position.
Hope that made sense…