Any UI code running on a modern CPU should take close to 0ms to update, no matter how many buttons, toggles, sliders and shadows.
For the rendering part, it depends, I'd say it should take between 0.5 and 2ms with many layers, a lot or transparency and not much care for optimization.
For the rendering part, it depends, I'd say it should take between 0.5 and 2ms with many layers, a lot or transparency and not much care for optimization.