Well if he doesn't get the interview at Google, he'll probably need to wait at least a year and a half before he can try again. So a few months of boning up on the material could save him a year and a half wait before trying a second time.

But generally you're right, he should apply sooner than later. But it's not worth it without feeling pretty solid on the material that's public knowledge that they quiz you on.

(I'm someone who only had a week and a half to prepare for my interview at Google and I don't recommend that little preparation)