I think you have it backward. It's not about how long after you think of clicking do the action happen, it's how long after you did click can your brain start to see the result on screen. With that 100 ms you mention, and let's add another 100ms by the software, you get 200 ms between the time your brain wants to click and the time it start receiving a visual response (assuming that part is immediate, which it is not). It is actually a big selling point of google chrome, while a lot of it isn't really that much faster, it do seems instant and firefox does not (at least for some people, including me).