Rupert, not timing. i have seen Ikeda sensei done it with uke claimed down on one of his finger and he was still able to do it. he didn't try to move the arm. he moved you. i might be able to do it with 2 fingers, on a good day.
I know what you mean. But I say, in the type of practice I showed, maybe you should try to break his finger. And I mean, snap it. And if you fall down, then yes, what he did must be worth learning. It's a different kind of practice. Not just holding. There are several kinds of training and you have to discern which is which and what useful purpose it serves.
I've just come from an all day long high school wrestling competition, so you might understnd where I'm coming from. Some of these boys have more dynamic aiki (really using their opponents FORCE, because the FORCE is real) than many Aikido sensei, in my opinion.