Neat concept, I like the delayed results meaning you have to time it right.
I think it would be cool if those only lasted for a couple seconds though, meaning you really had to time it. Like the light would turn green, but only for 2 seconds, so you couldn't just click on it from far away.
The inclusion of already green lights to throw off the player is a good idea.
The art is simple, but pleasing. It all fits together niceley.