The instructor can do a lot to help make it count, or at any rate to not get in the way. There is nothing so exasperating as finally getting to the dojo and getting in maybe 30 minutes on the hour of actual practice.
I'm a big fan of longer classes for exactly this reason. Three classes a week gets me nine practice hours. That's a much better return on the time spent driving to and from, changing, warming up, etc. than I would get if classes were only an hour long.