Yeah,it measures the time between the end of their mistake and when you interrupt them. There is a small window to get a perfect score, but yeah I'm thinking that window was a little too small.
I had to look up who Marty Armstrong was lol I've never played Lisa but I've heard very good things about it. I based all the art off of Earthbound characters. I styled the pianist after a friend of mine and gave him a funky shirt.