I don't think shorter periods are better. Our periods are 1 hour (or 55 minutes, I can never really tell), five periods a day, and I'm fine with them like that. It means that even if we go off-topic there's still time to learn the work we should, and if the teacher's late, the period isn't completely wasted.
I have a friend who's periods are half an hour long, and if the teacher was 10 minutes late, they could barely learn anything. Not to mention all the trouble of setting up computers and such.
I read that students were supposed to study in 50 minute sessions, so that sounds about the ideal length of a period. Anything shorter and it isn't productive. Anything longer and your attention tends to wander.